Application Of Hyperbranched Polymers In Leather Industry

　　 1 Preface

Today, how to improve the utilization rate of chrome tanning agents and reduce the heavy metal content in waste liquid has become a hot topic for leather tanning and environmental workers. In recent years, the synthesis of hyperbranched polymers has become an important research direction. In this paper, the types and properties of hyperbranched polymers are briefly introduced, especially the synthesis methods of hyperbranched polymers and their advantages and disadvantages.

　　 2 synthesis of hyperbranched polymers

The unique properties and simple synthesis methods of hyperbranched polymers make it a hot topic in the field of new chemical materials. As hyperbranched polymers can be obtained by one-step direct polymerization, industrial scale production may be achieved. The synthesis methods of hyperbranched polymers are polycondensation, ring opening polymerization and self condensation vinyl polymerization (SCVP) of ABX (X > 2) monomers.

2.1 one-step synthesis method

One step method refers to the one-step reaction without the control of ABX monomer. That is to say, the monomer and "nuclear compound" are all fed into the reactor at the beginning, depending on the number of times needed. Shu and so on take 5- phenoxy phthalic acid as AB type monomer, with phosphorus pentoxide and methanesulfonic acid as condensation agent, a hyperbranched polyether ketone with carboxylic terminus was synthesized by one-step method, and aromatic ketone bonds were formed by electrophilic aromatic substitution reaction. The degree of branching is about 0.155 measured by HNMR. One step is the most commonly used and more mature method to synthesize hyperbranched polymers. The advantage is that the synthesis method is simple and generally needs no gradual separation and purification. Polymers can still maintain many structural characteristics and properties of tree like macromolecules. The disadvantage is that polymers with polydispersity are often obtained, and the molecular mass can not be controlled. However, because of its simple and clear mechanism, convenient operation, mild reaction and wide source of monomers, it is still one of the most important means of synthesizing hyperbranched polymers.

2.2 quasi one step synthesis method

The so-called "quasi one step method", that is, the latter generation is synthesized by adding monomers (not adding cores) to the previous generation. The use of "one-step method" is beneficial to enable the functional groups that are added later to have more opportunities to react with functional groups on the backbone, and avoid condensation reactions of monomers to a greater extent, thus obtaining hyperbranched molecules with better molecular mass dispersion. Liu Lixin et al. Synthesized AB type monomers with 1 carboxyl groups and 2 hydroxyl groups by using maleic anhydride and glycerol as raw materials. Then pentaerythritol was used as the "nuclear molecule". When the ratio of pentaerythritol to maleic anhydride and glycerol mixed monomer was 1:100 and 1:150, the hyperbranched polyester with good water solubility at room temperature was obtained. The ratio of pentaerythritol to maleic anhydride and glycerol was two.

2.3 self condensation vinyl polymerization

In 1995, Frecher and so on reported a new method for synthesizing hyperbranched polymers, called self-condensing vinyl polymeriza-tion (SCVP). Self condensation vinyl polymerization is in the self condensation activity free radical polymerization, monomer is both initiator and branching point, vinyl monomer activation under external excitation, produce a number of active radicals, forming a new reaction center, triggering the next reaction. Hong Chunyan and so on have prepared hyperbranched polymers by using acrylic acid (2- bromo propanoyl) ethyl ester and methyl acrylate in the presence of four functional initiator. It is found that in the free radical polymerization, the chain of growth always maintains the activity of monomer reaction, and there is no chain transfer and chain termination process, so the concentration of the active chain remains unchanged. 2-4 ring opening polymerization has been widely used in the synthesis of hyperbranched polymers by ring opening polymerization. Ring opening polymerization is a kind of synthesis method which is completely different from traditional condensation polymerization. The monomer used is usually oxygen heterocyclic compound containing hydroxyl group. Compared with traditional condensation polymerization, the advantage of ring opening polymerization is that it does not need to exclude low molecular compounds and easily get polymer compounds in the process of synthesis. Liu Xiao Tian laughed at Novozyme435 lipase catalyzed the ring opening polymerization of caprolactone (epsilon -CL) catalyzed by hydroxyethyl methacrylate, and obtained the product of straight chain polycaprolactone with one end of double bond and hydroxyl at the other end. Finally, the hyperbranched structure of polystyrene -b- polycaprolactone product was obtained.

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2.5 ionic polymerization

Ionic polymerization includes cationic polymerization and anionic polymerization. Bochkarev and other anionic polymerization methods were used to synthesize hyperbranched polymer of three (five fluorophenyl) germanium halide, which produced a metal perfluorinated benzene ring active anion through the deprotonation of three ethyl amine. Then the hyperbranched structure was obtained by nucleophilic substitution of the perfluorinated benzene ring. In recent years, many methods have been developed for the development of hyperbranched polyphenylene, polyester, polyether, polyamine, polyamide, polyurethane, polysiloxane and vinyl monomers hyperbranched polystyrene. Hydroxypropyl methacrylate, such as Jia Zhifeng, was used to prepare hyperbranched polymethacrylate with hydroxyl terminated by self-condensing vinyl oxyanionic polymerization. The polymer with high molecular weight was obtained by using potassium hydride and crown ether complex as initiator.

2.6 other polymerization methods

In addition to the above synthetic methods, there are also hyperbranched polymers such as group transfer polymerization, stable radical polymerization, atom transfer radical polymerization, self addition vinyl radical polymerization and other hyperbranched polymers in leather. The unique structure and properties of hyperbranched polymers are closely related. Through the synthesis of hyperbranched polymers with different structures and the modification of their terminal groups, a variety of new polymer materials with special uses can be prepared, which make hyperbranched polymers have great application value and development potential in leather industry, attracting more and more researchers to intervene in this field.

3 applications of hyperbranched polymers

3.1 use of main tanning agent and retanning agent.

Hyperbranched polymers contain a large number of active peripheral functional groups with high reactivity. These end group functional groups can be chemically bonded with active groups (such as hydroxyl, amino, carboxyl groups) on the skin collagen fibers to form strong chemical bonds, which can be used as the main tanning agents for leather or fur. The use of hyperbranched polymers as retanning agents can give leather some special retanning effects, such as soft and plump, better elasticity, and better determination and absorption of tanning agents. For example, Jin Liqiang and other ethylenediamine and methyl acrylate as raw materials to synthesize 0.5 to 3.5 generation of dendrimer polyamide macromolecules, under alkaline conditions hydrolysis, the functional groups of their peripheral to carboxyl group, and the coordination with CrC3 to obtain metal coordinated dendrimer tanning agent. If the hyperbranched polymer is further modified, various properties of retanning agents can be made. In addition, hyperbranched polymers can also be used to modify glutaraldehyde, increase the bonding point with leather fibers, and improve the low temperature, yellowing and tear strength of glutaraldehyde tanning. For example, Wang Xuechuan and other end hydroxyl hyperbranched (amide ester) polymers were modified by anhydrous glutaraldehyde, and hyperbranched polymer leather retanning agents were obtained. When used for retanning of two layers of wet blue leather, the tensile strength of the finished leather after retanning is basically the same as that of phenolic aldehyde tannin PE-210, and the tear strength of the finished product is as high as 59.67N/mm.

3.2 used as finishing agent.

Because the chain of hyperbranched polymer chains is not easy to cause chain entanglement, when the relative molecular mass increases or the concentration increases, it can maintain low viscosity, so that it has unique leveling property and good film forming property. At the same time, hyperbranched polymer surface has a large number of end group active groups and special branching structure. The adhesion between coating and leather will be very firm. The coating is not easy to fracture and bears high folding fastness. Fluorocarbon polymers are widely used because of their high surface activity, outstanding chemical inertness and good biocompatibility. If the fluorocarbon chain is grafted onto hyperbranched polymers via chemical reaction, it will produce unique properties and can be applied in leather chemicals. Li Ming and other old protection methods protect the hyperbranched polyglycidyl outer hydroxyl, the internal hydroxyl reaction first, then protect the external hydroxyl solution, then participate in the reaction, so that more hydroxyl groups participate in the reaction, the reaction rate increased from 22.8% to 40.5%, and the hyperbranched polymer with fluorocarbon chain as the terminal group was successfully synthesized. The product is used as a finishing agent, which can overcome the shortcomings of traditional leather finishing agents such as chemical resistance, weatherability, compatibility and anti-aging. At the same time, because of its low viscosity, it can be used in conjunction with other finishing agents, so as to reduce the amount of organic diluent or do not use organic diluent. It is a green leather finishing agent with excellent performance. Wang Xuechuan et al. Graft polyurethane prepolymer onto hyperbranched polymer to obtain a hyperbranched polymer with low viscosity. The remaining end group of hyperbranched polymer is used for curing, which not only shortens the curing time, but also improves the crosslinking density of the cured film and the performance of the paint film. The performance of the finishing agent is stable, the leather coating is smooth and bright, the adhesion between the coating and leather is strong, the coating is not easy to break, the fastness to folding is high, and the curing time can be shortened.

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3.3 used as high absorptive chrome tanning AIDS.

Hyperbranched polymers have a large number of end group functional groups, which can be complexed with Cr (III) and other metal ions. They can be used as high absorptive chrome tanning AIDS or instead of chrome tanning agents to produce white wet skin, which can reduce the amount of chrome tanning agents and chromium pollution. Compared with the common high absorption chrome tanning AIDS, the hyperbranched polymers have more complexing groups, and the effect of absorbing and fixing chromium may be better. At the same time, the chromium salt can be saved, the chromium pollution in water will be reduced, and the environment can be protected, so that the effect of killing two birds with one stone can be achieved. Such as Qiang Xi Huai et al. A hyperbranched polymer (HTH P) with terminal hydroxyl group was synthesized by one-step process from cyanuric chloride and three phenol in acetone with K2CO3 as an acid binding agent. It is used as a chrome tanning additive in leather chrome tanning process. The results showed that HTHP had a significant effect on increasing the absorption and fixation of chrome salt by skin collagen. When the dosage of HTHP was 1%, the content of Cr2O3 in chrome tanning effluent decreased from 1.42 g/L without adding HTHP to 0.60g/L, and the shrinkage temperature of green leather increased from 90 to 94 degrees. After adding HTHP, the absorption of dyestuff and fatliquoring agent is improved, the color of the leather is strong, and the bath color is light and clear. Fan Guiyang et al. By repeated addition of Michael and amination reaction, the branched polyamines (PAMAM) of different branches were prepared. The PAMAM of the half generation was hydrolyzed under acidic conditions to prepare PAMAM-COOH with terminal group carboxyl group. It is found that PAMAM-COOH can be coordinated with chromate to form macromolecular metal complexes, and the alkali resistance of chromium salt is improved obviously after coordination. Wang Xuechuan and so on synthesized a hyperbranched polymer from butylene anhydride and two ethanolamine by "quasi one step method", and then reacted with maleic anhydride to obtain a hyperbranched polymer chrome tanning agent. Two The chrome tanning AIDS had the best effect before adding chromium powder. When the dosage was 1%, the content of Cr2O3 in chrome tanning waste liquor could be reduced by 45%. The addition of hyperbranched polymer chrome tanning agent can ensure the fine grain of leather and improve the Ts of tanned leather. Hyperbranched polymers are of great potential to be used as high absorptive chrome tanning AIDS. Therefore, it is of great significance for the development of leather industry to actively carry out the research work and develop new products and expand their application in leather industry.

3.4 used as levelling agent and fixing agent.

Hyperbranched polymer molecules have special cavities which bind the dye molecules or combine their active groups with dye molecules to control the release rate of dye molecules under suitable conditions. A large number of active groups on the periphery can be complexed with metal complex dye active groups, and can also be used for leather indole, so as to achieve the effect of leveling and fixing. If the hyperbranched polymer is applied to blend modification of polypropylene fiber, the dyeability of polypropylene fiber can be greatly improved. The hyperbranched polysulfone amine was used for small molecule loading, and it was found that they had strong loading capacity for water-soluble dyes such as Congo red, methyl orange and tiger red. The dyeing properties of silk fabrics modified by amino group hyperbranched compounds were obviously improved, and their rubbing fastness, color fastness and levelling performance were satisfactory. Using these research methods, hyperbranched polymers can also be used for leather dyeing. However, the application of hyperbranched polymers as leather levelling agents and indole agents has not been reported much.

3.5 other uses

In addition to the above uses, hyperbranched polymers can also be used as slow release agents, flocculants for treating tannery sewage or formaldehyde capture in leather industry. Polymer flocculants can be used to accelerate the settlement of suspended solids only in a small amount, and therefore they are increasingly widely used in sewage treatment. Hyperbranched polymers are large molecules and have active groups that can be complexed with heavy metals. Therefore, heavy metal ions such as chromium, calcium and magnesium ions can be complexed in tannery sewage. The peripheral ions of hyperbranched polymers can also be designed to combine with sulfur ions (S2-), which can greatly reduce the amount of sulphur pollution produced in leather factories. Hyperbranched polymers can also be used to capture free formaldehyde in leather to reduce formaldehyde content in leather. For example, Wang Xuechuan and other two monomers were prepared by Michael addition reaction with ethanolamine and methanolamine as raw materials. A terminal hydroxyl hyperbranched poly (amine ester) (HPAE) was prepared by transesterification of monomer and nucleus (three hydroxymethyl propane) under p-toluene sulfonic acid catalyzed by one-step method. Using malonate two ethyl ester, the anionic K2CO3 catalyst was used to modify the end group of HPAE by transesterification, thus preparing hypermethylene like hyperbranched polymer (HPAM). The application of HPAM to the capture of free formaldehyde in aldehyde tanning leather (pigskin) was studied. The capture rate of formaldehyde reached 56.25% and the capture effect was obvious.

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　　 4 Conclusion

Hyperbranched polymers have unique structural properties and wide application prospects. However, the synthesis and characterization are still the main research work. The polymerization of hyperbranched polymers has become a flourishing and high-profile field in synthetic chemistry, and its application fields are constantly expanding. It is believed that hyperbranched polymers are one of the most competitive and promising polymers in the future.

With the increasing maturity of hyperbranched polymers and the understanding of their properties, hyperbranched polymers will be developed in the following directions: improving synthetic methods, enriching the types of hyperbranched polymers, establishing new theoretical systems and characterization methods, expanding and deepening application research, and further increasing the way to prepare hyperbranched macromolecules and obtaining functional hyperbranched polymers. It will provide new ideas and simple and feasible technical routes for leather auxiliaries such as retanning agents and finishing agents, so as to promote the rapid development of leather industry in China.