In the production of waterborne polyurethane, carboxylic acid, as an anionic hydrophilic chain extender, is a kind of carboxylic acid with binary alcohol. With its unique molecular structure, excellent product performance has been widely used.
Carboxylic acid chain extender mainly consists of 2,2-dihydroxymethyl propionic acid (DMPA) and 2,2-dihydroxymethyl butyric acid (DMBA), which is a unique multifunctional hindered diol molecule with both hydroxyl and carboxyl groups. To improve the adhesion of coatings and dyeing properties of synthetic fibers, and to increase the alkali solubility of coatings. It can be used in water-soluble polyurethane system, water-soluble alkyd resin and polyester resin, epoxy coatings, polyurethane elastomer and powder coatings.
It can also be applied to leather chemicals, liquid crystals, inks, food additives, adhesives and chemical industries. Especially in the manufacture of waterborne polyurethane and leather finishing agents, it is not only a chain extender, but also a good self emulsifying property of polyurethane, which can greatly improve the stability of polyurethane emulsion and is widely used. Application.
II. Advantages of Dihydroxymethyl Carboxylic Acid
Waterborne polyurethane emulsion usually introduces hydrophilic agent into polyurethane molecular chain, then neutralizes it with alkali, and disperses in deionized water by mechanical agitation to form polyurethane water emulsion.
The hydrophilic agents used in waterborne polyurethane are mainly anionic, cationic and non-ionic. The main anionic types are: 2,2-dihydroxymethyl propionic acid, 2,2-dihydroxymethyl butyric acid, tartaric acid, butanediol sulfonate, sodium ethylenediaminoethyl sulfonate, glycerol and maleic anhydride, etc. The cationic types are methyl diethanolamine, triethanolamine, etc. The non-ionic types are hydroxyl-terminated polyethylene oxide.
Non-ionic hydrophilic agents, such as polyethylene oxide, must have a high content in order to stabilize the dispersion. Waterborne polyurethane resin with hydroxyl polyoxyethylene ether as hydrophilic group has good electrolyte resistance, but poor water resistance, so it is not practical.
Cationic hydrophilic agents such as ethylenediamine sodium adduct as the hydrophilic compound make the whole reaction system alkaline, not only with the rapid reaction of NH2 base and NCO group, but also with the reaction of NCO and NHCOO, so the reaction is difficult to control, easy to gel, and the emulsion particles are coarse and film resistant. The water quality is poor, so it can not be used in industry.
The dimethoxylated carboxylic acids in anionic type contain two hydroxyl groups, and they also act as chain extender. This dual effect makes it show great superiority in the preparation of self emulsifying PU emulsion. In the process of carbamate synthesis, it makes the reaction system acidic. Under acidic conditions, the reaction of NCO and OH is mild, while NHCOO - does not participate in the reaction, and does not cause the gel. In addition, Dihydroxymethyl carboxylic acid also acts as chain extender, so that hydrophilic group (i.e. carboxyl group) is located in the macromolecule chain. Waterborne polyurethane resin with excellent stability, water resistance and solvent resistance can be prepared by using tertiary amine as neutralizer. Dihydroxymethyl carboxylic acid is the best hydrophilic compound widely used in the preparation of waterborne polyurethane resin.
Tris, 2,2-dihydroxymethyl propionic acid (DMPA) and 2,2-dihydroxymethyl butyric acid (DMBA)
Among these two kinds of Dihydroxymethyl carboxylic acids, 2,2-dihydroxymethyl propionic acid has been used for a long time, and it is a hydrophilic chain extender widely used at present. Although it has many advantages, there are still many shortcomings, mainly because of its high melting point (180-185 C), it is difficult to heat melting, which requires the addition of organic solvents such as N-methyl pyrrolidone (NMP), N.N-dimethylamide (DMF), acetone, etc., while the high boiling point of NMP makes it difficult to remove APU. Moreover, DMPA has a low solubility in acetone, which requires a large amount of acetone to be added in the synthesis process. The process of ketone removal not only wastes energy, but also brings potential safety hazards. Therefore, the use of 2,2-dihydroxymethylpropionic acid not only produces high energy consumption, but also causes organic residues in products.
2,2-dihydroxymethyl butyric acid (DMBA) is a new hydrophilic chain extender which has been rising in recent years. Compared with 2,2-dihydroxymethyl propionic acid, 2,2-dihydroxymethyl butyric acid has the following advantages:
1. It has better solubility in organic solvents. The following table shows the solubility data of DMBA and DMPA in different temperatures and solvents.
Data sheet of solubility of DMBA and DMPA in different temperatures and solvents:
Solubility: unit g/100g solvent
The solubility in water is 48% for DMBA and 12% for DMPA.
2. High reaction rate, fast reaction speed and low reaction temperature. For example, the reaction time of synthetic polyurethane prepolymer is short, generally only 50-60 minutes, while that of DMPA is 150-180 minutes.
3. for waterborne polyurethane emulsion, its particle size is finer and its distribution is narrow.
4. Low melting point, 108-114 C;
5. The diversity of formulations can reduce the use of solvents, thus reducing the cost of solvents and the cost of waste liquid treatment.
6. It can be used to prepare completely solvent-free polyurethane and polyester systems.
In the actual synthesis process, it does not need to consume a little solvent. The emulsion has good performance and excellent mechanical properties. It not only shortens the reaction time, reduces energy consumption, but also saves energy. Therefore, 2,2-dihydroxymethyl butyric acid is the best hydrophilic compound known at present. Industry experts believe that Dihydroxymethyl butyric acid is a green chemical that will replace Dihydroxymethyl propionic acid.
Development of Dihydroxymethyl Carboxylic Acid in China
The development and production of 2,2-dihydroxymethylpropionic acid in China started late. This is mainly restricted by the process of water-borne resin in China. The industrialized production of 2,2-dihydroxymethylpropionic acid in China began in 1995. In the 21st century, the demand for 2,2-dihydroxymethylpropionic acid has increased year by year, and a certain market scale has been formed. But unfortunately, the production of 2,2-dihydroxymethylpropionic acid in China has not yet formed a scale. There are few manufacturers producing 2,2-dihydroxymethylpropionic acid, and the scale of production is relatively small. At present, the use of 2,2-dihydroxymethylpropionic acid in China mainly depends on imports.
2,2-dihydroxymethyl butyric acid (2,2-DMBA) has been restricted in production, development and application because of its complex production process, difficult industrialization, high production cost, high price and serious environmental problems. The production of 2,2-dihydroxymethyl butyric acid in our country started in 2006, and there are few manufacturers, but all of them have been shut down because of the above reasons. As a result, there is no 2,2-dihydroxymethyl butyric acid available in our country in recent years. As a result, many water-based materials manufacturers are waiting for feeding. They are eager to change this passive situation and expect to use 2,2-dihydroxymethyl butyrate as soon as possible. Acid.
Jiangxi Jiyu New Materials Co., Ltd. was founded under this background. At present, the newly built Jiyu 2,2-dihydroxymethylbutyric acid production workshop has reached 1200 tons per year, and the 2,2-dihydroxymethylpropionic acid production workshop has reached 3500 tons per year. Jiyu Company is determined to revitalize China's 2,2-dihydroxymethylbutyric acid and 2,2-dihydroxymethylpropionic acid industry, to make its due contribution to China's water industry and environmental protection industry.