Advances in the applications of synthetic phosphates

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The last edit to this post was made by That makes sense on 2012-8-1 at 09:01. 1 Introduction: The molecular structure of synthetic phosphates can be designed according to various applications and requirements, resulting in a wide range of structural and functional characteristics. This allows synthetic phosphates to compensate for the shortcomings of natural phospholipids in certain aspects, and combining the two can yield optimal performance in applications. Typically, synthetic phosphates, just like natural phospholipids, possess excellent wetting properties, cleaning capabilities, solubilizing effects, emulsifying and dispersing properties, as well as antistatic characteristics. They also have good resistance to acids and bases, a wide temperature range of operation. Compared to conventional anionic surfactants, they offer better resistance to electrolytes, hard water, and ionization. They are biodegradable, have low irritation levels, and are widely used in industries such as textiles, printing and dyeing, plastics, papermaking, leather processing, and household chemicals. Due to their structural differences, they possess distinct properties and are used in various applications; they are often employed in the production of additives such as detergents, emulsifiers, penetrants, antistatic agents, flame retardants, defoamers, fatting agents, plasticizers, and metallurgical extractants. As a chemical additive for leather processing, we make use of its excellent emulsifying and dispersing properties, wetting capacity, resistance to electrolytes and hard water, as well as its good compatibility, antistatic properties, flame-retardant characteristics, and easy biodegradability. 2 Applications of Synthetic Phosphates 2.1 Synthetic Phosphates as Components in Leather Fatting Agents Due to their amphiphilic structure similar to that of natural phospholipids, synthetic phosphates possess extensive resistance to acids, bases, and salts. When used as leather fatting agents in conjunction with chromium tanning agents or chromium retanning agents, they help promote the absorption of chromium salts by the leather. The phosphate groups contained in them can form complexes with chromium in the leather, resulting in a permanent fatting effect. They are suitable for the production of various wash-resistant leathers as well as those that require high fogging resistance. After fat addition, the finished leather exhibits high fullness, elasticity, and a silky feel, as well as certain hydrophobic properties. Combining it with natural phospholipids can compensate for its deficiencies in softness, moisture, and waxy texture. Phosphate ester fatting agents are usually synthesized using long-chain fatty alcohols or fatty alcohol ethers, as well as hydroxyl-containing natural oils such as castor oil, rapeseed oil, sunflower oil, cottonseed oil, fish oil, and lanolin. Before the phosphorylation reaction, long-chain fatty alcohols or fatty alcohol ethers, as well as hydroxyl-containing natural fats, are appropriately modified through reactions such as transesterification, amidation, sulfonation, quaternization, sulfation, halogenation, and etherification. This allows for the introduction of additional active groups or the exposure of existing active groups, followed by the phosphorylation reaction. By optimizing this combination effectively, the synthesized phosphates exhibit optimal fat-liquoring properties. Some use synthetic phosphates directly as fatting agent products; for example, the phosphate fatting agent PES is a product obtained by phosphorylating modified castor oil using phosphoric acid as the phosphorylating reagent. This product has good emulsifying properties, disperses easily in cold water, and is readily absorbed. When fat is added, it gives the leather fullness and elasticity, as well as a fine and dense grain structure. However, it has been found that it is advisable to use it in combination with fatting agents that possess excellent softness and moisturizing properties. Lan Yunjun and others used castor oil, as well as the products obtained from the transesterification of castor oil with rapeseed oil using low-carbon alcohols, as the main raw materials. By controlling the conditions of the synthesis process, they prepared PVO series of phosphorylated vegetable oil fatting agents whose main component is phosphorylated monoester (MAP). Tests have shown that it has good stability. Synthetic phosphates, used as fatting agents for leather, possess significant advantages in terms of emulsibility, penetration, filling capacity, water resistance, and antibacterial properties; however, they are inferior in terms of softness and moisturizing effect. Used alone as a leather fatting agent, its fatting effect is not satisfactory. It is usually combined with natural phospholipids and modified natural phospholipids, sulfated, sulfonated, or highly sulfite-treated animal and plant fats and oils, mineral oils, softeners, special surfactants, and other components to produce products with various fat-adding functions. Zhang Tingyou and others used phosphoric acid to replace part of phosphorus pentoxide in order to synthesize alkyl phosphates with a high esterification rate and a high MAP content. By combining these alkyl phosphates with modified natural fats and synthetic fats, an excellent leather waterproofing fat was obtained. It not only has excellent water resistance, but is also plump, soft, and elastic, with a strong silk-like feel, and bonds firmly to leather. It provides water resistance by reducing the critical surface tension of the leather fibers and causing expansion and blockage upon absorption of water. The advantage is that no heavy metal salts are required for fixation after fat addition, and it has a strong chemical bond with the collagen fibers of the leather. Bai Qingquan used two methods to synthesize the phosphate ester component: one involved reacting higher carbon alcohols with phosphorylating agents to produce fatty alcohol phosphates, which were then neutralized using triethanolamine. Another method involves the reaction of AEO with a phosphorylating reagent to produce fatty alcohol polyoxyethylene ether phosphates, which are then neutralized using triethanolamine. By controlling the molar ratio of fatty alcohols or AEO to P2O5, a mixture of monoesters and diesters of phosphoric acid in a specific proportion is obtained. A composite phospholipid fatting agent is then prepared using natural soybean phospholipids, synthetic phosphates, and deeply sulfited oils as the main components, with 0.3%–0.5% preservative added as well. The resulting composite phospholipid fatting agent PPC is resistant to acids, bases, salts, and electrolytes, and exhibits good stability at low temperatures. The leather treated with fat has a soft, plump, and elastic texture; its surface is smooth and oily without being greasy, with distinct pores. During dyeing and fat treatment, the dyes distribute evenly and penetrate deep into the leather, resulting in leather with excellent physical properties. It also effectively prevents the appearance of oil spots, greasy residues, and floating oil. Li Guangping et al. used a combination of synthetic phosphates and modified products of natural phospholipids; specifically, peanut oil residues were hydroxylated and modified, then mixed in certain proportions with modified castor oil phosphates, along with an appropriate amount of preservative, to produce the composite phospholipid fatting agent. Application studies show that it has good softening and filling properties. Wang Xuechuan and others modified fish oil through amidation to obtain alkanolamides containing active groups such as amide and hydroxyl groups; subsequent phosphorylation and neutralization reactions were carried out, after which these compounds were combined with various active ingredients, thereby enabling the multifunctionality of the fatting agent through synergistic effects. The resulting modified fish oil phosphorylated fatting agent exhibits stable performance and excellent fatting properties. After being treated with this fatting agent, the leather becomes soft, plump, and elastic, while also possessing a certain degree of luster and smoothness. The amide group in alkanolamides has a strong affinity for leather fibers, enabling high absorption and conferring softness and a natural luster to the leather. 2.2 Applications of phospholipids as flame retardants: Macromolecular phosphates have low volatility, good stability, and are difficult to burn; they can endow products such as plastics, rubbers, synthetic fibers, coatings, and leather with flame-retardant properties. They can overcome some of the shortcomings of currently used phosphorus- and halogen-based flame retardants with good flame-retardant effects, such as low molecular weight, tendency to migrate out of the products, decomposition temperatures lower than the ignition temperature of the materials, susceptibility to decomposition under the influence of light and oxygen, toxicity or corrosiveness, and poor compatibility with the materials being flame-retarded or with other additives. Moreover, phosphates are easily biodegradable; under photocatalysis, they break down into CO2 and phosphate ions, have very low toxicity, and do not cause pollution during production and use. Guo Rui et al. prepared dimethyl phosphite by reacting phosphorus trichloride with methanol; in the presence of a strong base (sodium alkoxide), it was subjected to a conjugate addition reaction with acrylamide to yield 3-(dimethoxyphosphoryl)propanamide, which was then hydroxymethylated with formaldehyde to produce the flame retardant N-hydroxymethyl-3-(dimethoxyphosphoryl)propanamide. Its flame-retardant mechanism lies in its ability to rapidly decompose at high temperatures to produce organic phosphoric anhydrides or phosphoric acid, thereby causing the fibers to dehydrate and carbonize. The phosphoric anhydrides form a glass-like molten substance during thermal decomposition, which covers the fabric and facilitates the direct oxidation of organic materials into CO2, thus suppressing the generation of flammable gases. The bond between the flame retardant and cellulose prevents cellulose from breaking down at high temperatures, thereby stopping the formation of levoglucose. The unsaturated double bonds formed through dehydration cause the fiber molecules to cross-link with each other, turning them into non-flammable carbon compounds; this prevents smoldering and thus effectively inhibits the progression of combustion. Zhou Xiaojun used urea, phosphoric acid, and PVAc in a condensation reaction to produce nitrogen-containing phosphate ester polymer flame retardants. This flame retardant exhibits excellent flame-retardant properties. Studies on the flame-retardant treatment process for fabrics and the key performance indicators show that it meets the requirements specified in standard GB5454‑85. It features low cost, versatility, simple processing, and ease of industrialization, overcoming the disadvantages of low-molecular-weight flame retardants such as poor heat resistance and tendency to decompose during processing. The synergistic effect between phosphorus and nitrogen significantly enhances the flame-retardant effect. Bao Zhisu introduced a polyaryl-silicon-containing macromolecular diphosphate ester that not only possesses excellent flame-retardant properties, but also features high thermal stability, low volatility, good compatibility with resins, no impact on processing properties, as well as durability, light resistance, and water resistance. It also serves as both a stabilizer and a dispersant, and can be widely used for flame retardancy in thermoplastic and thermosetting resins. The synthetic conditions for these macromolecular polyaryl silicon-containing diphosphates are simple, making them easy to produce. It contains no halogens, and it is expected to soon become one of the excellent phosphate ester flame retardants that will be sought after by manufacturers. 2.3 Applications of phosphates in antistatic agents: Antistatic phosphates mainly include alkyl phosphates and alkyl ether phosphates. Alkyl phosphate antistatic agents not only possess excellent antistatic properties but also have functions such as emulsification, rust prevention, and dispersion, allowing for a wide range of applications; in addition to the textile industry, they can also be used as antistatic agents for leather and plastics. The main components are monoesters and diesters, with monoesters having better antistatic properties than diesters. Diesters can endow fabrics with excellent smoothness and a low coefficient of friction, which helps to reduce the generation of static electricity. The ratio of monoester to diester in alkyl (ether) phosphate esters also affects their properties: a higher content of monoesters results in good antistatic properties but poor smoothness, while a higher amount of diesters gives good smoothness but reduced antistatic performance. Alkyl phosphate anionic antistatic agents can be divided into two categories based on the length of the alkyl chain: low-carbon alcohol phosphates and high-carbon alcohol phosphates. Low-carbon alcohol phosphates are generally alcohols with 12 carbon atoms or fewer, produced using a phosphoric acidification process with phosphorus pentoxide. The actual production process requires addressing issues such as the color of the product, the control of the ratio between mono- and diesters, and the stability of the composition; it can be applied in oils for dry-spun polyester and fine-denier polypropylene. Low-carbon alcohol phosphate esters have good antistatic properties, but poor smoothness; the fibers feel rough to the touch, become sticky at high humidity, and their antistatic properties decline significantly at low humidity. For example, C12 alkyl phosphates possess excellent antistatic properties, but they absorb moisture easily; once moistened, their viscosity increases, which leads to excessive adhesion between fibers, resulting in fiber entanglement and breaks. This makes them unsuitable for the high speeds required in new manufacturing processes. High-carbon alcohol phosphates generally have carbon chains of 18 atoms or more, possess high melting points, and are a type of new antistatic agent. High-carbon alcohol phosphate esters have slightly poorer antistatic properties, but they offer good smoothness, resulting in fibers that are soft and smooth to the touch. High-carbon alcohol phosphates such as C18 and C20 are solids at room temperature. Spinning oils based on these compounds, after drying, can form a solid lubricating film on the surface of fibers, thereby reducing stickiness. Moreover, an increase in chain length enhances smoothness, giving the fibers a better feel. The antistatic properties of alkyl ether (or polyether) phosphate salts are primarily related to the length of the alkyl carbon chain. The ether linkage has a relatively minor impact; it is less sensitive to temperature and humidity, and it has good compatibility with polyether monomers. The antistatic effect of alkyl phosphates is highly dependent on relative humidity; at lower relative humidity levels (40%), their antistatic performance is poor. At a relative humidity of 45% to 65%, monovalent alkyl phosphates have better antistatic effects than dialkyl phosphates. The properties of phosphates are related to the type of neutralizing agent used; for example, sodium phosphates result in better smoothness of the fibers compared to potassium phosphates, but they offer poorer antistatic properties. Alkyl ether phosphates are common components in short-fiber oil agents; as the number of ethylene oxide groups increases, the smoothness improves, but this has little effect on antistatic properties. The greatest advantage of alkyl ether (or polyether) phosphates is their good compatibility with polyethers; they can possess the properties of both polyethers and phosphates. They exhibit excellent antistatic and heat-resistant characteristics, making them one of the focus areas in international research on phosphates in recent years. The technical core lies in the structure of the polyether and the control of the ratio of phosphoric ester monoesters to diesters. Although anionic phosphate surfactants have the disadvantages of relatively poor hardness resistance and inability to be used under extreme pH conditions, they remain excellent antistatic materials. Quaternary ammonium-type cationic surfactants possess significant antistatic properties, but they also have obvious drawbacks: they can cause dyes to change color, reduce lightfastness, and cannot be used in the same bath as anionic additives, dyes, or brighteners. Phosphate-based amphoteric surfactants precisely compensate for the disadvantages of the aforementioned two types of surfactants, while enhancing their advantages. The application of phosphate-based amphoteric surfactants in the printing and dyeing industry is receiving increasing attention. 2.4 Phosphates are used as penetrants, leveling agents, dispersants, and other additives. As penetrants and dispersion aids, the main types of phosphates are isooctyl phosphate and isooctyl polyoxyethylene ether phosphate. The cloud point of isooctyl phosphate is above 80 °C, and it is widely used due to its advantages such as high solubility, resistance to hard water, acidity, and high temperatures, as well as strong emulsifying and dispersing properties and excellent wetting capacity. Sodium dioctyl phosphate and sodium di(2-methylhexyl) phosphate, prepared by phosphorylating octanol and dimethylhexanol, are often used as defoamers, penetrants, and wetting agents. Triisobutyl phosphate, when properly combined with non-ionic surfactants, can be used to produce defoaming wetting agents. Alkyl polyoxyethylene ether phosphates are widely used in pre-treatment processes for printing and dyeing due to their good water solubility, moderate foam and penetration properties, as well as high solubility and stability in alkaline solutions. Yang Jingxin et al. formulated an alkali-resistant penetrant NT by combining the isooctyl polyoxyethylene ether phosphate salt produced by the reaction of isooctyl polyoxyethylene ether with P2O5, with sodium secondary alkyl sulfonate SAS60. A mixture of 13% sodium polyoxyethylene ether phosphate of isooctanol and 13% SAS60 achieves a alkali resistance of 200 g/L and a penetration time of 17 s, making it suitable for fabric pretreatment processes involving high concentrations of caustic soda. Yang Haibo et al. applied the synthesized isooctyl phosphate ester as a penetrant in the ceramic glaze infiltration process, solving the problems of penetration depth and color saturation gradient of the glaze. The optimal content of the penetrant in the penetration-promoting mixture is 2% to 3%, which results in red stained vitrified tiles with relatively ideal gradients in color, penetration depth, and color saturation. These tiles combine the wear resistance, corrosion resistance, acid-alkali resistance, dirt resistance, and high flexural strength of natural granite and porcelain-colored tile materials, with the rich decorative effects of natural marble and printed glazed tiles. They have a smooth texture that is elegant and luxurious; after polishing, they become as smooth as a mirror, offering a beautiful and sophisticated appearance. Thus, they represent an ideal decorative material. Qiang Xihuai et al. synthesized and introduced the application of isooctyl phosphate penetrants in leather production. In wet processing, phosphate penetrants exhibit good penetration in neutral and alkaline solutions, and can be widely used in processes such as soaking, ash dipping for depilation, deliming, and neutralization. In dry processing, it can act as a leveling agent for coatings, ensuring that the film formed after coating is smooth and even. This prevents the coating from sagging and reduces surface irregularities, thereby helping to improve the quality of the coated layer. Phosphates are used as surfactant dispersants in coatings, enhancing the gloss and colorability of the coatings, improving surface wettability, and providing more stable dispersion. In water-based formulations, the amount of phosphate surfactants used is generally 0.2%–0.5% of the solid content, and they are added during dilution or grinding. Adding it at any time during the production process of latex paint yields good results. During the base material preparation stage, it can function both as an emulsifier and as a pre-polymerization stabilizer. Experiments have shown that phosphates can act as dispersant stabilizers to prevent flocculation; adding phosphates during the dilution stage of paint formulations can achieve this effect. Phosphate molecules have a good affinity for inorganic pigments. At room temperature, phosphate ester surfactants exhibit slightly better anti-adhesion properties compared to other surfactants, and this improvement is more significant at 48.9 °C. Phosphate surfactants perform excellently in improving gloss, enhancing color stability, improving substrate wettability, and enhancing cleaning power. The presence of phosphate groups also prevents flash rusting that may occur on metal surfaces before the water-based coating dries, without altering the medium shear viscosity (KU) and high shear viscosity (I-CI) of the coating formula. These characteristics are of great significance as a reference for applying them to pigment pastes, leather fillers, and composite resin coatings. 3 Conclusion The applications of phosphates are far from limited to these; for example, oxidized corn starch phosphates are used in the food industry as stabilizers, thickeners, additives, flavorings, etc. By adding an appropriate amount during production, they can improve the quality of the final products and effectively enhance the quality of foods. Oxidized corn starch phosphates can also be used in the paper industry as reinforcing agents for cardboard, as surface sizing agents for printed paper, and as pigment binders for copperplate paper. The above discussion is only relevant to the application aspects of dermatised products that can serve as a reference. Used in food, health products, and pharmaceutical additives, natural phospholipids possess unique advantages; whereas when used as industrial additives in textile dyeing, flame retardants, coatings, ceramics, etc., synthetic phosphates offer greater versatility and are more advantageous. As additives in leather processing products, a combination of natural and synthetic phospholipids is required to achieve satisfactory results.