Hydrogen peroxide is a widely used chlorine free bleaching agent. It has the excellent characteristics of high whiteness and good whiteness stability of bleaching products, no release of toxic gases in the bleaching process, no corrosion to equipment and little environmental pollution. It is suitable for bleaching a variety of fibers and adopting a variety of processing processes. However, hydrogen peroxide decomposes slowly under the condition of low temperature and low alkali, and the bleaching rate is low. Therefore, when using hydrogen peroxide to bleach fabrics, it usually needs to be carried out in the reaction system of high temperature and high alkali, resulting in problems such as high energy consumption, serious pollution and fiber damage. This is contrary to the requirements of energy conservation and emission reduction, improving product quality and bringing high economic benefits to enterprises advocated by today’s society. In order to reduce oxygen bleaching energy consumption and reduce fiber damage, many printing and dyeing workers are committed to studying new additives and new processes for low-temperature oxygen bleaching. The main way to realize hydrogen peroxide low-temperature bleaching is to develop hydrogen peroxide bleaching accelerators, mainly including activators and catalysts.
In recent years, it has been found that peroxidases produced by some microorganisms (such as laccase, manganese peroxidase and lignin peroxidase) can catalyze the decomposition of hydrogen peroxide, which has a good application effect in low-temperature bleaching of cotton fabrics. However, the application of natural enzymes is limited due to some problems. The use of imitation enzyme as the decomposition catalyst of hydrogen peroxide can provide a new direction for the realization of low-temperature oxygen bleaching. Enzyme like metal complex catalysts can react with peroxides to produce intermediates with strong bleaching ability. The intermediates react with pigments and recover to original substances after effective bleaching, which can act repeatedly; It has the advantages of low dosage, high catalytic efficiency, high whiteness of bleached fabric, small damage and soft hand feeling, and has a good application prospect. At present, the research hotspots of enzyme like catalysts mainly include metal phthalocyanine complexes, metal porphyrin complexes, Schiff base metal complexes, macrocyclic polyamine metal complexes and so on
Metal phthalocyanine complex
Metal phthalocyanine complexes have macrocyclic conjugated structure, fairly uniform electron cloud density distribution, very stable molecular structure, acid resistance, alkali resistance, heat resistance and insoluble in water. The peroxide anion reaction of metal complexes and hydrogen peroxide dissociated from hydrogen peroxide catalyzes the decomposition of hydrogen peroxide, and finally generates high active substances such as hydroxyl radicals to destroy the pigment and achieve the purpose of bleaching. In order to improve the bleaching efficiency of fabrics and reduce the production cost, Ren et al. Synthesized metal phthalocyanine complex copcr as oxygen bleaching catalyst and applied it to hydrogen peroxide low-temperature bleaching process. The results show that compared with the traditional high-temperature and strong alkali oxygen bleaching process, the whiteness of cotton fabrics treated with copcr as oxygen bleaching catalyst, working solution pH = 9.5, temperature 80 ℃, stacking for 60 minutes is increased by 6.9%, strength retention is increased by 7.9%, and gross efficiency is the same, The cottonseed shell is less. It can be seen that the application of metal phthalocyanine complex as catalyst in hydrogen peroxide low-temperature cold reactor bleaching process not only reduces the temperature and pH of bleaching process, but also obtains good bleaching effect and achieves the purpose of energy saving and consumption reduction.
Metalloporphyrin complex
The most studied metalloporphyrin complexes are iron porphyrin complexes and manganese porphyrin complexes. At present, metalloporphyrin complexes are widely used in the field of pulp, mainly to replace lignin peroxidase to catalyze the degradation of lignin. Shimada et al. Studied the reaction mechanism of iron porphyrin simulating lignin peroxidase and confirmed that iron porphyrin can oxidize lignin model compounds. Crestini et al. Found that manganese porphyrin complexes have stronger degradation ability of lignin than iron porphyrin complexes, because manganese porphyrin complexes have better stability under oxidation conditions. However, the cost of metalloporphyrin complexes is high, and it is difficult to prepare chiral complexes. At the same time, metalloporphyrin complexes can degrade carbohydrates, which brings some difficulties to practical application.
Schiff Base Complexes
Schiff base mainly refers to a class of organic compounds containing imines or connected with imine characteristic groups. It is formed by condensation of amines and active carbonyls. The manganese complex of Schiff base has a good effect in low temperature bleaching of textiles. Schiff base and its metal complexes have high catalytic activity and are mostly used in the field of biomimetic catalysis. Due to the poor water solubility of most complexes, it is difficult to be applied to the system with water as the medium, which affects the catalytic activity of the complexes, resulting in certain restrictions on their popularization and application. Therefore, the design and synthesis of water-soluble Schiff alkali metal complexes has become a hot spot
Nitrogen containing macrocyclic metal complexes
Nitrogen containing macrocyclic metal complexes contain multiple nitrogen coordination heteroatoms on the ring skeleton composed of carbon atoms. The lone pair electrons of nitrogen atoms cross and overlap, which makes the macrocyclic ring have high electron cloud density, so they can form stable complexes with metals. In the washing industry, nitrogen-containing macrocyclic metal complex catalysts are used as dye transfer inhibitors to prevent white or light colored textiles from being polluted. The whiteness of low-temperature catalytic bleaching fabric is equivalent to that of traditional high-temperature bleaching fabric, and the fabric has good wettability and strength retention. Low-temperature bleaching has significant energy-saving advantages。
The research on hydrogen peroxide bleaching accelerators is still developing. The research direction is to develop eco-friendly and efficient oxygen bleaching accelerators and develop composite and synergistic oxygen bleaching accelerators, so that the new hydrogen peroxide / accelerator system can effectively reduce the decomposition activation energy of hydrogen peroxide when the amount of activator is small, greatly reduce the bleaching temperature, and have no obvious damage to the strength of bleached fabrics, It is better to realize one bath treatment of cotton fabric desizing, boiling and bleaching, so as to achieve the purpose of energy conservation, emission reduction, quality improvement and efficiency
