Application Of Sol-Gel Technology In Leather Market

< p > 1. The principle and process of sol-gel method < /p >

< p > the basic principle of sol-gel technology: with inorganic salts or metal alkoxides as precursors, a homogeneous solution is formed in suitable solvents (water or organic solvents), the precursor is hydrolyzed (or alcoholysis) under the action of the catalyst, and then condensed into nano sized particles to form sols. The particle size of the products is usually within the range of 1~100 nm.

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< p > the basic reaction process of hydrolysis and condensation process: < /p >

< p > (1) hydrolysis reaction (taking metal alkoxide as an example) < /p >

< p > the extent of the reaction depends on the dosage of H2O. If the molar ratio of water is more than 4, it can be hydrolyzed completely to produce M (OH) 4.

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< p > (2) polycondensation reaction < /p >

< p > condensation reaction can be divided into water loss polycondensation and loss of alcohol polycondensation. The degree of condensation will directly affect the particle size, stability and reactivity of sol particles.

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< p > 2. The stability of sol is less than /p.

< p > 2.1 sol stability theory < /p >

< p > sol has many kinds and wide uses, but no matter what kind of sol, its stability has always been the main research content of researchers.

According to DLVO theory, the sol system is a multiphase system with a certain degree of dispersion. It has huge surface area and surface energy. Therefore, thermodynamically speaking, it is an unstable system, and the particles tend to sink each other and reduce their surface energy.

On the other hand, because particles are small and have strong Brown motion, they can prevent their sedimentation in gravity field, so sol is a stable system in dynamics.

The former is considered to be the main one, so most sol can not be preserved for a long time.

Taking silica sol as an example, its surface contains a large number of hydroxyl groups, and has a high reactivity. If the inhibitor is not added to the storage process, gel can be formed in a short time (10 d), so it is quite necessary to discuss its stability.

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< p > many scholars have studied the sol theory deeply.

F.Dumont demonstrated in detail the applicability of DLVO theory in the stability of silica sol. He believed that the classical DLVO theory had little explanation for the stability of silica sol. To accurately explain the stability of silica sol, the electrostatic repulsion force and Vander Waals attraction should be considered simultaneously.

Thomas W.Healy studied the effect of 1-1 valence electrolyte and pH on the stability of silica sol. On this basis, a model based on polysilicate surface steric hindrance and cationic exclusion was introduced to control the gelation. He hoped that the proposed electrostatic impedance model could provide a new direction for the stability study of silica gel.

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< p > 2.2, the effect of sol-gel is less than /p.

< p > 2.2.1 solvent, water and catalyst < /p >

< p > when sol-gel technology is used to synthesize the products, besides solvent, water and catalyst are the main raw materials, which will directly determine the stability of the products, which is the most important factor in many influencing factors.

Most of the solvents are ethanol, which allows the precursor, water and catalyst to disperse evenly in the homogeneous solution to ensure that the three can react at the molecular level.

The experimental results showed that the gel time of silica sol grew longer with the increase of ethanol dosage.

Wang Xingli thinks that with the increase of ethanol content, the dielectric constant of the solution increases, the thickness of the double layer of the colloid is thickened, and ethanol is the hydrolysate of ethyl orthosilicate, which inhibits the hydrolysis. Therefore, the gel time of the sol increases.

The effect of water on the stability of sol is very important, because in the process of reaction, water is both a hydrolytic reactant and a condensation product.

Yang Jing explored the effect of water content on the sol-gel time. The experiment showed that the gel time of water / ester molar ratio (Rw) decreased first and then increased in the range of 1~10, and the gel time of Rw=7.2 was the shortest.

When the amount of water is very small (Rw<4), the reaction is dominated by hydrolysis, polycondensation reaction is inhibited, gel time is longer, and after Rw>4, hydrolysis of tetraethyl orthosilicate has been completely hydrolyzed. The reaction time will mainly take polycondensation reaction, and the gel time will naturally shorten. When water continues to increase to Rw>7.2, the interaction between silica sol particles will be enhanced due to the dissolution effect, so gel time will start to increase.

In the literature, the role of the catalyst is explained. Under acidic conditions, H+ will protonate the OR group of tetraethyl orthosilicate (TEOS) molecule. H2O molecules attack the silicon atoms with strong electronegativity and form metastable pition states with coordination bonds. Subsequently, the OH group of water molecules replace the TEOS OR group and undergo hydrolysis reaction.

If there is no catalyst, TEOS will not react for a long time after mixing with water.

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< p > 2.2.2 particle size, pH and electrolyte < /p >

< p > sol is thermodynamically unstable system, and sol particles are metastable. Even if the dosage of reactant is better than the choice, the products synthesized by sol-gel technology will still gel gradually. During this process, particle size, pH and electrolyte are the key factors affecting the stability of sol.

He emphasized the effect of silica particle size on its stability. He thought that increasing the particle size of silica particles could improve the stability of high concentration acidic silica sol.

Under the same silica concentration, the smaller the distance between particles, the total potential energy will decrease rapidly due to the decrease of the distance between particles, and the stability of silica sol will also decrease rapidly. Conversely, with the increase of silica sol particle radius, the smaller the particle surface activity, the larger the distance between particles, the smaller the interaction force between particles, the more stable the silica sol will be.

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The effect of < p > pH and electrolyte on sol stability is due to the change of Stern double layer of colloidal particles, but their specific effects are different.

Lu Yichun studied the effect of pH on the stability of alkaline silica sol (pH=9.5). It was found that in the range of 3.5~7.5 due to the compression of H+ on the electric double layer, the stability of sol decreased obviously, and the double electric layer structure with opposite and stable electric conductivity was formed after pH<3.5, and the sol was new and had good stability in the range of 3.5~7.5.

Wang Jinxi studied the effect of electrolytes on the stability of silica sol. It was found that in the near neutral environment, the lower the electrolyte concentration and the longer the gelation time, the better the sol stability. However, when pH<2 or pH>11, the electrolyte had little effect on the stability of silica sol. He explained that there was already a high concentration of electrolyte in the sol under such pH, and the effect of external salt on the total electrolyte concentration was very small, so the stability was not very different.

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< p > 2.2.3 additive < /p >

< p > in order to improve the stability and film forming properties of silica sol, many scholars have achieved the above goal by adding some or some additives.

At present, the methods of improving the sol stability by additives can be broadly classified into 4 categories: the first is to add some active substances in the sol to reduce the active groups on the surface of the sol particles and reduce the chemical activity of the surface, so as to prevent the sol from settling.

For example, Ye Yu Zo and so on, using gamma methacryl oxy propyl trimethoxy silane (KH- 570) as modifier, using twelve alkyl sulfate (SDS) instead of cosolvent, under magnetic stirring, adding 0.4 g KH- 570 to SDS containing silica sol, and then stirring at room temperature for 12 h, the KH- 570 modified silica sol was prepared. The stability of the silica sol was improved obviously. The second group added some substances that could change the structure of the double layer of the colloidal particles in the sol, and improved the stability of the sol by changing the zeta potential.

For example, Tian Lipeng and so on have studied the influence of surfactants on the viscosity and stability of silica sol.

The results show that anionic surfactants can reduce the viscosity of alkaline silica sol and improve the stability of silica sol. The cationic surfactant has the opposite effect on the alkaline silica sol. The third is to increase the stability of sol by using composite sol.

Wang Qing and other butyl titanate and zinc acetate were used as precursors to prepare TiO2/ZnO composite sol by sol-gel technology.

The results showed that the stability of TiO2/ZnO composite sol increased with the increasing proportion of ZnO, and the amount of glacial acetic acid increased gradually. The fourth was to prepare organic sol-gel sols by using organic solvents instead of water.

Ren Zhijun mixed water sol and glycol at a certain ratio, adding tetrahydrofuran with 15% mass fraction as azeotropic agent, vacuum distillation, and adding suitable stabilizer to prepare glycol nano silica sol.

The zeta potential of the hydrosol is - 8.6 mV, while the glycol nano silica sol can reach - 23 mV, and the stability is obviously improved.

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< p > 3. The application prospect of sol-gel in < a href= "http://www.91se91.com/" target= "_blank" > leather < /a > fixing color < /p >

< p > leather dyeing is a very important process in the water stage of leather. It can give leather different colors and increase its commercial value.

The dyes commonly used in leather are acid dyes and direct dyes. These two dyes are fixed on leather fibers only by Vander Ed Ley and hydrogen bonds. Because of the sulfonic group and carboxyl groups of dyes, they are easy to be dissolved in water when encountering water, so the wet rubbing fastness is poor.

In order to solve the problem of fastness of leather dyeing, besides developing new dyes with strong coloring ability, we should also start the research and development of harmless and efficient fixative.

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< p > the development of leather fixative has gone through 3 stages. First types of reactive fixing agents developed in the 80s of last century, such fixing agents have obvious effect of fixation, but most of them can produce formaldehyde at reaction time, which is very harmful to human body. The second type of fixing agent is cationic fixing agent, which can form complex with dye anions and improve dyeing fastness.

The third types of fixing agents are organic silicon fixing agents, polyurethane fixing agents and nano fixing agents. These fixative agents are harmless and highly efficient, and are the main research directions of leather fixative in the future.

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< p > Luo Min mentioned in his article for the first time that silica sol can improve the color fastness of < a href= "http://www.91se91.com/" target= "_blank" > textile > /a >, which provides a new research method for fixing color.

Since then, many papers have begun to introduce the application of silica sol in textile color fixing.

Ren Baoyong and other 7 cationic dyes and 7 basic dyes were used to dye the silk. The silica sol prepared by hydrolysis of tetraethyl orthosilicate was used to fix the color. It was found that the soaping fastness of the 8 dyes was increased by 1~2 grade, and the remaining dyestuffs soaping fastness increased by more than 3 grade.

Rhododendron and so on have discussed in detail the factors affecting the fixation effect of silica sol on direct dyes. The data indicate that the sol of acidic catalyst is better than that of alkaline catalyst, and that the hydrolysate of low temperature hydrolysis is better than that of high temperature hydrolysis.

Silica sol can only be kept stable in a certain time range, and the storage time is too long, which will lose the fixation effect.

Yin Yunjie hybridized the Direct Scarlet 4BS to the silica sol and compared with the dyeing after fixing process. The Direct Scarlet 4BS hybrid silica sol can better improve the dyed fastness of the fabric, the K/S value of the dyed fabric is increased by 11.1%, and the dyed brightness of the fabric can also be improved.

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< p > the application of sol-gel method to prepare silica sol in leather fixation is still in exploration stage, but as mentioned above, the fixation effect of silica sol on textiles has been very obvious.

The mechanism of fixation is generally believed that the sol-gel process can form a discontinuous film on the fibers. If the film is dense enough, the dye molecules on the dyed fabric can be prevented from leaving the fabric.

The analysis shows that the application of sol-gel technology in leather fixing is also highly operational and feasible.

First, the morphology of collagen fibers and fabric fibers of leather is similar. Some fabric fibers, such as protein fiber and nylon, are all the same as leather fibers. Therefore, a similar fixation effect will be produced. Secondly, the dyeing mechanism of leather and textiles is very similar. They are divided into 3 processes: adsorption, diffusion and fixation.

In addition, the binding mechanism between dyes and fibers is similar. They can be summarized as follows: ionic bonding, hydrogen bonding, van Dewali interaction, covalent interaction and so on. Thirdly, referring to the above silica sol fixation mechanism, although leather fixation can not be dyed and dyed like textiles, but it can be adjusted by sol-gel process to synthesize silica sol. First, inhibit its hydrolysis, add it in the later stage of leather dyeing process, and then form a dense color film on the leather surface by in-situ formation, so as to achieve the purpose of fixing silica sol.

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< p > we can see that the application of silica sol in leather dyeing is of great research space. We are exploring the application of silica sol in leather dyeing and fixing.

There is no literature report on the application of silica sol in leather dyeing at present. It is hoped that this will provide a new research direction for leather fixation technology, so as to promote the development of dyeing process cleanliness.

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