NL2036751B1

NL2036751B1 - Preparation method of modified sepiolite-based composite pigment

Info

Publication number: NL2036751B1
Application number: NL2036751A
Authority: NL
Inventors: Zhao Yukai; Liu Yang; Li Zixiu; Hu Xiayi; Wang Wenqiang
Original assignee: Chinese Res Acad Env Sciences; Univ Xiangtan
Priority date: 2024-01-05
Filing date: 2024-01-05
Publication date: 2025-07-22

Abstract

U I T T R E K S E L The present disclosure provides a preparation method of a modified sepiolite—based composite pigment, and relates to the field of preparation of composite pigments. Chitosan, sepiolite and an acetic acid solution are mixed and stirred, to obtain a stirred product and the like. By means of the present disclosure, heat stability and weather resistance of an organic pigment can be improved. (+ Fig. 2)

Description

P1959/NLpd

PREPARATION METHOD OF MODIFIED SEPIOLITE-BASED COMPOSITE PIGMENT

TECHNICAL FIELD

The present disclosure relates to the field of preparation of composite pigments, in particular to a preparation method of a modified sepiolite-based composite pigment.

BACKGROUND ART

Lead-chrome yellow pigments contain a lot of Pb, Gr and other heavy metals, such that serious heavy metal pollution will be caused due to the use of the lead-chrome yellow pigments. Compared to lead-chrome yellow inorganic pigments, bisazo organic pigments from benzidine yellow with chromaticity similar to lead-chrome yellow have excellent color properties and tinting power. However, organic pigments are in lack of good stability, dispersibility and weather resistance, which limits their applications in the indus- trial field. Thus, it is necessary to modify the organic pigments to improve their properties. At present, the properties of the or- ganic pigments are mainly improved by core coating, coating, sol- gel and synthesis methods. Among them, the most commonly used methods are core coating and coating methods, that is, the organic pigments are adsorbed by inorganic materials as inorganic cores and then coated with TiO,, lithopone, sepiolite and other coatings.

Both the sepiolite and SiC. are adsorbed onto pigment yellow 12 through electrostatic attraction, which not only synthesizes the advantages of stable structure and good dispersibility of Si0: and the sepiolite, but also retains the advantages of bright color and high hiding power of the pigment yellow 12, such that a chitosan- sepiolite/pigment yellow 12@Si0, composite pigment with excellent structural stability is formed.

The shortcomings in the prior art lie in that when composite pigments with high weather resistance are prepared through a shell-core method, the sepiolite is not modified, resulting in in- sufficient binding fastness of the organic pigments and adsorption sites of the sepiolite.

SUMMARY

In the present disclosure, chitosan and sepiolite are mixed, and an amino group of the chitosan in an acetic acid solution is protonated, and the protonated chitosan, serving as a polyelectro- lyte,binds to the negatively charged sepiolite. The chitosan has the advantages of chemical inertness, high biocompatibility, high mechanical strength, good film-forming property and low cost, and contains pendant amine and hydroxyl functional groups, so as to be attached to small/large molecules for chemical modification. The chitosan shows high whiteness, which has low influence on chroma- ticity of a prepared composite pigment, such that the modified se- piolite shows high mechanical strength, active binding sites are exposed, and absorption capacity for pigment yellow 12 is im- proved. Then, when the chitosan-modified sepiolite is mixed with an organic pigment, sodium dodecyl benzene sulfonate is added, negatively charged sulfonic acid groups exist on a surface of the sodium dodecyl benzene sulfonate, while amino groups capable of being protonated exist on a surface of the chitosan-modified sepi- olite, and the sodium dodecyl benzene sulfonate binds to the chi- tosan-modified sepiolite through charge attraction; and meanwhile, intermolecular hydrogen bonds are formed by hydroxyl and carbonyl groups existing in a molecular structure of the pigment yellow 12 and a large quantity of hydroxyl groups on the chitosan, resulting in a more uniform and compact binding, and dispersibility of a prepared chitosan-sepiolite/pigment yellow 12 composite pigment is obviously improved.

The sepiolite is a fibrous natural clay mineral rich in mag- nesium silicate. It has a uniform pore diameter, high specific surface area and excellent ion exchange capacity. The chitosan is basic polysaccharide abundant in nature, and contains a large amount of amino and hydroxyl groups on its molecular chains. The chitosan is used for modifying the sepiolite, so as to improve surface potential of the sepiolite, such that uniform positive charge exists on the surface of the sepiolite; and on the basis of keeping a sepiolite framework, vibration peaks of N-H and tele- scopic peaks of N-C=0 are obviously increased, which can provide more active potentials, thereby facilitating adsorption of the or-

ganic pigment.

When the composite pigment is prepared, the sepiolite is solely added to an organic pigment suspension for complete reac- tion with heating and subsequent centrifugal separation instead of being modified by the chitosan, however, this approach leads to a demixing phenomenon. As a result, the organic pigment cannot uni- formly wrap the surface of the sepiolite to form a composite pig- ment with a "shell-core" structure formed by coating the surface of the sepiolite as a core with the organic pigment.

The organic pigment is added to an appropriate surfactant, with regard to the phenomenon that the organic pigment is prone to agglomeration, surface potential of the organic pigment can be re- duced, as well as dispersion of the organic pigment in water can be promoted by adding the surfactant, a surface of the organic pigment is negatively charged, and the organic pigment binds to the chitosan-modified sepiolite with the positive surface charge, to form the stable composite pigment.

Advantages:

The process is simple, conditions are moderate, no Pb, Gr or other heavy metals are contained, and the composite pigment not only has chromaticity properties of the organic pigment, but also can improve heat stability and weather resistance of the organic pigment. The chitosan-modified sepiolite is used as an inorganic core and the organic pigment is used as a coating layer in the composite pigment, thereby reducing costs of the organic pigment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an FT-IR comparison diagram of sepiolite, chitosan- modified sepiolite, a composite pigment and pigment yellow 12 in

Embodiment 1;

FIG. 2 is a thermogravimetry diagram of a composite pigment versus pigment yellow 12 in Embodiment 1;

FIG. 3 is a stereogram showing calcination of a composite pigment and pigment yellow 12 in Embodiment 1 at different temper- atures for 2 h, where, a is pigment yellow 12, b is pigment yellow 12 calcined at 250°C for 2 h, c is a composite pigment, and d is a composite pigment calcined at 250°C for 2 h; and

FIG. 4 is a diagram showing an application experiment of a composite pigment and pigment yellow 12 in Embodiment 1, where, a is a wood board, b is an ABS hard plastic board, c is a PVC expan- sion sheet, the pigment yellow 12 is put on left sides of the dif- ferent substrates, and the composite pigment is put on right sides of the different substrates.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A ratio of a mass of chitosan to a mass of sepiolite to a volume of an acetic acid solution is preferably 0.1-0.2 g: 2 g: 200 ml. A particle size of the sepiclite preferably ranges from 15 pm to 18 pm. A mass percent of the acetic acid solution preferably ranges from 2% to 5%. Stirring time is preferably 6 h, and a stir- ring temperature preferably ranges from 20°C to 30°C. In chitosan- modified sepiolite, amino groups of the chitosan bind to siloxane and hydroxyl groups in the sepiolite through hydrogen bonds, such that the modified sepiolite has high mechanical strength of the chitosan and more active binding sites. The chitosan-modified se- piolite has higher stability and better heat resistance; and it is shown through characterisation that a rod-like structure of the chitosan-modified sepiolite becomes shorter and thicker, specific surface area becomes smaller, and surface potential becomes a pos- itive value.

A ratio of a mass of the chitosan-modified sepiolite to a volume of water to a mass of a pigment to a mass of sodium dodecyl benzene sulfonate is preferably 0.4-0.9 g: 100 ml: 0.1-0.6 g: 0.5 g. Reaction conditions preferably include: temperature of 70°C and time of 10 h. Drying conditions preferably include: temperature of 60-80°C and time of 12-24 h. The pigment preferably includes pig- ment yellow 12. It is shown through characterisation that a sur- face of a composite pigment prepared from modified sepiolite be- comes coarser, and is thicker and has a film-forming phenomenon compared to a structure of the chitosan-modified sepiolite, and surface potential becomes lower; and the composite material pre- pared from the modified sepiolite has higher acid, alkali and or- ganic solvent resistance and smaller mass loss under a thermogra- vimetry test compared to a composite pigment prepared from unmodi- fied sepiolite. In the present disclosure, by pretreating an or-

ganic pigment with an anionic surfactant, surface potential of the organic pigment can be reduced, so as to allow the organic pigment to better bind to the chitosan-modified sepiolite core, in addi- tion, the organic pigment can be better dispersed with the anionic 5 surfactant, so as to more uniformly wrap a surface of the chi- tosan-modified sepiolite, and a formed composite pigment is more uniform in color. The sodium dodecyl benzene sulfonate has good solubility at 60-80°C, and compared to a room temperature condi- tion, the organic pigment can be better dispersed in the surfac- tant at 60-80°C and experience a reduction in surface potential.

Embodiment 1 {1) 200 ml of solution containing 2 wt% of acetic acid was taken, 0.5 g of chitosan was added therein, a chitosan solution was obtained after ultrasonic dissolution with stirring, 2 g of sepiolite with an average particle size of 15-18 um was added to the chitosan solution with stirring at a room temperature for 6 h, and chitosan-modified sepiolite was obtained after centrifugal separation, washing and drying; and (2) 100 ml of deionized water was taken, 0.5 g of sodium do- decyl benzene sulfonate was added for dissolution, then 0.1 g of pigment yellow 12 was added, a suspension was obtained after mix- ing well, 0.9 g of chitosan-modified sepiolite was added to the suspension, the mixture was heated in a water bath for 70°C and subjected to a stirring reaction for 10 h, and the resulting prod- uct was dried at 60°C for 12 h after centrifugal separation and washing with deionized water, to obtain a composite pigment.

Weather resistance test: pigment yellow 12 with the same mass and the composite pigment in Embodiment 1 were selected and used to undergo a stability test experiment for 3 days in acid, alkali and an organic reagent with the same volume respectively, an acid- ic condition was a 1 mol/L HCl solution, an alkaline condition was a 1 mol/L NaOH solution, an organic reagent condition was absolute ethyl alcohol, and an ultraviolet spectrogram was obtained from the test.

FIG. 1 is ultraviolet absorption spectra of the pigment yel- low 12 and the prepared composite pigment in different solvents, and the ultraviolet absorption spectra of the composite pigment in different solvents at the same duration are lower than those of the pigment yellow 12 after the impregnation in different solvents of a 1M HCl solution, a 1M NaOH solution and absolute ethyl alco- hol for different durations, suggesting that chemical resistance of the composite pigment is superior to that of the pigment yellow 12.

FIG. 2 is a thermogravimetry diagram of the composite pigment versus the pigment yellow 12, total weight loss of the pigment yellow 12 reached 57.89% at 800°C, and total weight loss of the composite pigment was 24.15% at 800°C; and heat stability of the composite pigment was obviously improved after sepiolite adsorp- tion and SiC; coating, the weight loss of the pigment yellow 12 began to rapidly decrease from 230°C, while the weight loss of the composite pigment began to rapidly decrease from 250°C. Thermogra- vimetry results obtained in FIG. 2 were consistent with results of the stereogram showing calcination at different temperatures for 2 h in FIG. 3, a color of the pigment yellow 12 was deepened at 230°C, while a color of the composite pigment was not obviously changed at 230°C; and the color of the composite pigment was deep- ened at 250°C, such that the composite pigment was significantly enhanced compared to the pigment yellow 12 with reference to the thermogravimetry diagram and the stereogram.

Embodiment 2 (1) 200 ml of solution containing 3 wt3 of acetic acid was taken, 0.5 g of chitosan was added therein, a chitosan solution was obtained after ultrasonic dissolution with stirring, 2 g of sepiolite with an average particle size of 15-18 um was added to the chitosan solution with stirring at a room temperature for 6 h, and chitosan-modified sepiolite was obtained after centrifugal separation, washing and drying; and (2) 100 ml of deionized water was taken, 0.5 g of sodium do- decyl benzene sulfonate was added for dissolution, then 0.3 g of pigment yellow 12 was added, a suspension was obtained after mix- ing well, 0.7 g of chitosan-modified sepiolite was added to the suspension, the mixture was heated in a water bath for 70°C and subjected to a stirring reaction for 10 h, and the resulting prod-

uct was dried at 80°C for 18 h after centrifugal separation and washing with deionized water, to obtain a composite pigment.

Embodiment 3 (1) 200 ml of solution containing 3 wt? of acetic acid was taken, 0.5 g of chitosan was added therein, a chitosan solution was obtained after ultrasonic dissolution with stirring, 2 g of sepiolite with an average particle size of 15-18 um was added to the chitosan solution with stirring at a room temperature for 6 h, and chitosan-modified sepiolite was obtained after centrifugal separation, washing and drying; and (2) 100 ml of deionized water was taken, 0.5 g of sodium do- decyl benzene sulfonate was added for dissolution, then 0.2 g of pigment yellow 12 was added, a suspension was obtained after mix- ing well, 0.8 g of chitosan-modified sepiolite was added to the suspension, the mixture was heated in a water bath for 70°C and subjected to a stirring reaction for 10 h, and the resulting prod- uct was dried at 80°C for 18 h after centrifugal separation and washing with deionized water, to obtain a composite pigment.

Embodiment 4 (1) 200 ml of solution containing 5 wt% of acetic acid was taken, 0.8 g of chitosan was added therein, a chitosan solution was obtained after ultrasonic dissolution with stirring, 2 g of sepiolite with an average particle size of 15-18 pum was added to the chitosan solution with stirring at a room temperature for 6 h, and chitosan-modified sepiolite was obtained after centrifugal separation, washing and drying; and (2) 100 ml of deionized water was taken, 0.5 g of sodium do- decyl benzene sulfonate was added for dissolution, then 0.6 g of pigment yellow 12 was added, a suspension was obtained after mix- ing well, 0.4 g of chitosan-modified sepiclite was added to the suspension, the mixture was heated in a water bath for 70°C and subjected to a stirring reaction for 10 h, and the resulting prod- uct was dried at 80°C for 18 h after centrifugal separation and washing with deionized water, to obtain a composite pigment.

Embodiment 5 (1) 200 ml of solution containing 2 wt% of acetic acid was taken, 0.5 g of chitosan was added therein, a chitosan solution was obtained after ultrasonic dissolution with stirring, 2 g of sepiolite with an average particle size of 15-18 pm was added to the chitosan solution with stirring at a room temperature for 6 h, and chitosan-modified sepiolite was obtained after centrifugal separation, washing and drying; and (2) 100 ml of deionized water was taken, 0.5 g of sodium do- decyl benzene sulfonate was added for dissolution, then 0.5 g of pigment yellow 12 was added, a suspension was obtained after mix- ing well, 0.5 g of chitosan-modified sepiolite was added to the suspension, the mixture was heated in a water bath for 70°C and subjected to a stirring reaction for 10 h, and the resulting prod- uct was dried at 80°C for 24 h after centrifugal separation and washing with deionized water, to obtain a composite pigment.

Comparative Example 1

Other conditions are identical to those in Embodiment 3, ex- cept that sepiolite is not modified with chitosan in advance, and a specific process is as follows: 100 ml of deionized water was taken, 0.05 g of sodium dodecyl benzene sulfonate was added for dissolution, then 0.2 g of pigment yellow 12 was added, a suspension was obtained after mixing well, 0.8 g of chitosan-modified sepiolite with an average particle size of 15-18 um was added to the suspension, the mixture was heated in a water bath for 70°C and subjected to a stirring reaction for 10 h, and the resulting product was dried at 80°C for 18 h after cen- trifugal separation and washing with deionized water, to obtain a composite pigment.

In Comparative Example 1, the addition of the sepiolite to a suspension of the organic pigment for complete reaction with heat- ing and subsequent centrifugal separation will result in a demix- ing phenomenon, and consequently, the organic pigment cannot even- ly wrap the surface of the sepiolite to form a composite pigment with a "shell-core® structure formed by coating the surface of the sepiolite as a core with the organic pigment.

Comparative Example 2

Other conditions are identical to those in Embodiment 3, ex- cept that the organic pigment is not treated in advance, and a specific process is as follows:

(1) 200 ml of solution containing 3 wt% of acetic acid was taken, 0.5 g of chitosan was added therein, a chitosan solution was obtained after ultrasonic dissolution with stirring, 2 g of sepiolite with an average particle size of 15-18 um was added to the chitosan solution with stirring at a room temperature for 6 h, and chitosan-modified sepiolite was obtained after centrifugal separation, washing and drying; and (2) 100 ml of deicnized water was taken, 0.2 g of pigment yellow 12 was added, a suspension was obtained after mixing well, 0.8 g of chitosan-modified sepiolite was added to the suspension, the mixture was heated in a water bath for 70°C and subjected to a stirring reaction for 10 h, and the resulting product was dried at 80°C for 18 h after centrifugal separation and washing with deion- ized water, to obtain a composite pigment.

If the organic pigment is not pretreated with the anionic surfactant, the organic pigment has poor dispersibility in an aqueous system, and the organic pigment wraps the chitosan- modified sepiolite non-uniformly, such that the obtained composite pigment also has poor dispersibility.

Comparative Example 3

Other conditions are identical to those in Embodiment 3, ex- cept that the reaction is performed only at a room temperature, and a specific process is as follows: {1} 200 ml of solution containing 3 wt% of acetic acid was taken, 0.5 g of chitosan was added therein, a chitosan solution was obtained after ultrasonic dissolution with stirring, 2 g of sepiolite was added to the chitosan solution with stirring at a room temperature for 6 h, and chitosan-modified sepiolite was ob- tained after centrifugal separation, washing and drying; and (2) 100 ml of deionized water was taken, 0.05 g of sodium do- decyl benzene sulfonate was added for dissolution, then 0.2 g of pigment yellow 12 was added, a suspension was obtained after mix- ing well, 0.8 g of chitosan-modified sepiolite with an average particle size of 15-18 um was added to the suspension, the mixture was subjected to a stirring reaction at a room temperature for 10 h, and the resulting product was dried at 80°C for 18 h after cen- trifugal separation and washing with deionized water, to obtain a composite pigment.

If the reaction is not performed under the condition of heat- ing in the water bath, the surfactant has poor solubility, such that the obtained composite pigment also has poor dispersibility.

Application Experiment

Pigment yellow 12 and a CTS-sep/pigment yellow 12@Si0; compo- site pigment underwent a spraying experiment on different sub- strates through a spraying method, as shown in FIG. 4. In FIG. 4, the pigment yellow 12 is put on the left side, the CTS-sep/pigment yellow 1205850: composite pigment is put on the right side, images are spraying images of the coated composite pigment on a wood board, an ABS hard plastic board and a PVC expansion board sequen- tially from top to bottom, the coated composite pigment can be well sprayed on the wood board, the ABS hard plastic board and the

PVC expansion board and has the similar spraying effect to the pigment yellow 12, such that it can be proved that the composite pigment applied to wood materials, plastic and PVC substrates the same as the pigment yellow 12, and thus has a wide application range.

Claims

CONCLUSIONS

1. A method of preparing a modified sepiolite-based composite pigment, characterized in that it comprises the following steps: 1) mixing and stirring chitosan, sepiolite and an acetic acid solution, and centrifuging and drying a resulting stirred product, to obtain chitosan-modified sepiolite; and 2) mixing the resulting chitosan-modified sepiolite, water, pigment yellow 12 and sodium dodecylbenzenesulfonate for reaction, and centrifuging and drying a resulting reactant, to obtain the modified sepiolite-based composite pigment.

2. Preparation method according to claim 1, characterised in that in step 1), a ratio of a mass of chitosan to a mass of sepiolite to a volume of the acetic acid solution is: 0.1-0.2 g : 2 g : 200 ml.

3. Preparation method according to claim 1, characterised in that in step 1), a particle size of the sepiolite ranges from 15 µm to 18 µm.

4. A preparation method according to claim 1, characterised in that in step 1), a mass percentage of the acetic acid solution varies from 2% to 5%.

5. Preparation method according to claim 1, characterised in that in step 1), the stirring time is 6 hours and the stirring temperature ranges from 20 °C to 30 °C.

6. A preparation method according to claim 1, characterised in that in step 2), a ratio of a mass of the chitosan-modified sepiolite to a volume of water to a mass of the pigment to a mass of the sodium dodecylbenzenesulfonate is 0.4-0.9 g : 100 ml : 0.1-0.6 g : 0.5 g.

7. Preparation method according to claim 1, characterised in that in step 2), the reaction conditions comprise: temperature of 70 °C and time of 10 hours.

8. Preparation method according to claim 1, characterised in that in step 2), the drying conditions comprise: temperature of 60-80 °C and time of 12-24 hours.