Abstract: Fluorinated surfactants are important components of multifunctional fabric finishing agents. PFOS and PFOA are two harmful fluorinated surfactants that, due to their persistent environmental stability and high bioaccumulation, will be listed as persistent organic pollutants (POPs) by the United Nations and banned. The latest alternatives mainly focus on six aspects, namely the use of C6 or C4 fluorinated finishing agents, nano fluorinated finishing agents, compound fluorinated finishing agents, acrylic fluorocarbon ester resins, and polytetrafluoroethylene.

 Oforeword

Waterproof, oil repellent, and stain resistant multifunctional finishing can change the surface properties of textiles, making them less susceptible to wetting or contamination by water, oil, and stains. Currently, it has been widely used in various fields such as clothing fabrics, household fabrics (umbrella fabrics, tents, kitchen fabrics, dining table fabrics, decorative fabrics), industrial fabrics, labor protection fabrics, and military fabrics. Among numerous waterproof, oil repellent, and stain resistant finishing agents, the finishing agent based on fluorinated surfactants has the best effect. They are all organic fluoropolymers with perfluorinated or partially fluorinated side groups. Their backbone main chain itself does not contain fluorine, but it is a carrier of important polymer characteristics, affecting the formation, hardness, and fastness of polymer films on textile substrates. Perfluorinated or partially fluorinated side groups are reactive and can firmly fix polymers on textile substrates at high temperatures, making it difficult for oil, water, and stains to infiltrate and penetrate fibers. The research and development of this fluorinated multifunctional finishing agent is very active in various countries around the world. 3M and DuPont in the United States, Clariant in Switzerland, Asahi Glass and Daikin Industries in Japan, Atohem in France, and others have all developed corresponding products. China began researching it in the mid-1960s, but to this day, all perfluoroalkyl products used as raw materials are imported, and the domestic preparation technology is not yet mature. According to incomplete statistics, there are currently over 70 enterprises in China that process and produce this type of product, with an annual output of 1.1 million; 12000 tons, basically using: ① further producing new products on the basis of imported original products; ② Made by diluting 121 original products; ③ Made by simply compounding imported original products; ④ Selling products of foreign companies on a commission basis. Only 3% to 4% of enterprises introduce foreign production technology for self-produced products. In addition, 5% to 6% of products in the Chinese market are directly sold by foreign companies.

1Special Fluorinated Surfactants for Textile Applications and Existing Problems

1．1Special fluorinated surfactants for textile use

Preparation of fluorinated multifunctional finishing agents using fluorinated surfactants, in which all hydrogen atoms on the carbon hydrogen chain in the molecule are replaced by fluorine atoms. The special fluorinated surfactants currently used in the printing and dyeing industry are mainly hydrophobic carbon chain perfluorinated chemicals, such as nC8F17SO3Na, nC7Fl5COOH，nC7F15CONH(CH2)3N(CH3)3。 I and nC10Fl9O (c2H4O) 23C10Fl5, etc. The following methods are generally used for manufacturing in industry.

1．1．1Electrolytic Fluorination Method

Alkyl carboxylic acids are electrolyzed in anhydrous hydrogen fluoride medium, and the hydrogen atoms on the alkyl group are replaced by fluorine atoms to produce perfluoroalkyl acyl fluorides, also known as Simous fluorination method:

CH_2n+lCOOH + (2n+2)HF(point solution)→  CnF_2n+ICOF

When alkyl acyl chloride or alkyl sulfonyl chloride is used instead of alkyl carboxylic acid for electrochemical reaction, higher yields of perfluoroalkyl acyl fluoride can be obtained:

nC₇F₁₅COCl    (HF)→nC₇F₁₅COCF

nC₈FSO₂Cl    (HF)→nC8F17SO2F

1．1．2Aggregation method

This method is based on the production of tetrafluoroethylene, starting from halogen exchange reaction:

CHC1₃  +  2HF——CHClF2  +  2HC1

2CHC1F2  (Heating)→F2C  +   2HC1

The produced tetrafluoroethylene acts as a modifier in the polymerization process, undergoing the following free radical initiated polymerization process:

(1)Synthesis of Perfluoroalkyl Iodine

5CF2==CF2+IF5+2I2——C2F5I

(2)Adjusting aggregation

C2F5I+(n一1)CF2==CF2F(CF2 ——CF2)nI

(3)Termination

F(CF2—CF2)nI+CH2==CH2→F(CF2一CF2)nCH2CH2I

The general formula of perfluoroalkyl based polymer iodide is CnF_2n+1C2H4I, in which the iodine atom is separated from the perfluoroalkyl group by a methylene group, making it easy to react with nucleophiles (perfluoroalkyl iodine cannot directly react with nucleophiles such as OH -, NH3, etc., nor can it be directly converted into intermediates of multifunctional finishing agents with carbon fluorine chain structures). The resulting intermediate or final active component of the multifunctional finishing agent is the fluorinated surfactant, such as

Perfluoroalkyl based polymer (methyl) acrylate formula: R=- H, CH3

In the process of manufacturing perfluorinated surfactants using the polymerization method, the wastewater generated can be treated using traditional wastewater treatment techniques, namely mechanical, chemical, and biological processing three-stage wastewater treatment technology, which is also an advantage of the polymerization method.

1．1．3Aggregation method

Perfluoroalkenes such as tetrafluoroethylene and hexafluoropropene can polymerize into oligomers in the presence of catalysts such as potassium fluoride and cesium fluoride. When tetrafluoroethylene oligomers, pentamers account for more than 50%, while tetramers, hexamers, and heptamers each account for 10% to 15%. The resulting products are isomerized olefins and do not produce monoolefins; When hexafluoropropylene oligomers, a mixture of dimers and trimers is obtained, both of which are alkene structures. They can further synthesize a series of fluorinated surfactants.

1．2Existing Problems

The above three methods for manufacturing special fluorinated surfactants have the following problems:

(1)The perfluorinated surfactant produced by the electrolytic fluorination method is a complex of different carbon chains. The reaction is intense and the carbon chain is prone to breakage. Therefore, in addition to the main product, there are also short chain perfluorinated compounds and other by-products in the reaction products, with a yield of only 10% to 30%. Therefore, few companies use this method to manufacture fluorine-containing finishing agents.

The polymerization method is difficult to control due to the use of polymerization agents to polymerize perfluorinated olefins. Therefore, the hydrophobic based carbon chain perfluorinated surfactants produced are a mixture of perfluorinated surfactants with different carbon chain lengths, with a chain length distribution of 4— 14 or 6-12. The most common chain length is usually 8— 10, especially with surfactants containing 8 carbon atoms, the yield is relatively high, ranging from 65% to 70%. So, most companies in the world that produce fluorine-containing finishing agents use this method, such as Daikin Industries, Asahi Glass, DuPont, Clariant, and Atochem.

The product obtained by the oligomerization method is a mixture of perfluoroolefin oligomers composed of dimers, trimers, tetramers, and pentamers.

(2)Side reactions may occur during manufacturing

When using the polymerization method to produce perfluoroalkyl based polymer iodides, side reactions may occur, such as the formation of perfluorooctanoic acid (PFOA).

(3) The fluorinated surfactant produced will decompose

For example, perfluoroalkyl based polymer (methyl) acrylate will decompose in the environment to produce PFOA, and for example, waterproof and oil repellent finishing agents using perfluorooctyl sulfonyl (PFOS) as the main active component will eventually produce PFOS again after chemical decomposition or biodegradation.

(4)Perfluorosurfactants need to be made into emulsions or dispersed suspensions before they can be used. To meet the requirements of multifunctional textile finishing, suitable high-efficiency emulsifiers are usually used to stabilize perfluorinated surfactants. In the past, alkylphenol polyoxyethylene ether (APEO) was commonly used, but due to its serious harm to the ecological environment and human health, it has been adopted. Fatty acid polyoxyethylene ether (non-ionic surfactant) or quaternary ammonium salt (ionic surfactant) and a mixture of several surfactants can be used as substitutes.

2 列入POPsFluorinated surfactants for textile use listed as POPs

The Organization for Economic Cooperation and Development (OECD) and the Scientific Committee on Health and Environmental Risks (SCHER) have conducted research on fluorinated surfactants used in textiles and found that the two most commonly used perfluorinated surfactants on the market, perfluorooctane sulfonate (PFO) and perfluorooctanoic acid (PFOA), pose potential hazards to human health and the ecological environment

2．1PF0S

At room temperature and pressure, it is a solid. The vapor pressure at 2O ℃ is 3.31X10^-4Pa. The solubility in water at (20+ 0.5) ℃ is 519mg/L, and the pK is 3.27. Its chemical structural formula is:

In the formula: X=ONa, halogen, amine. The most commonly used perfluorooctane sulfonamide derivative finishing agent is usually prepared by reacting perfluoroalkyl sulfonamide halides with ethylamine, ethanolamine, etc., and then introducing acrylic acid. The chemical composition is N-ethyl acrylate and N-ethyl perfluorooctane sulfonamide. Dicguard F-88 from DaiNippon Ink Co., Ltd. has this structure. The multifunctional fabric finishing agents based on fluorinated surfactants developed or used by some enterprises in China are made from fluorooctane sulfonyl fluoride as the starting material, and then reacted with acrylic acid derivatives to produce N-alkyl-N-hydroxyalkyl perfluorooctane amides. Its waterproof and oil repellent performance is related to the length of carbon, which can be solved by using acrylic acid derivatives or acrylic acid derivatives and polyurethane derivatives as comonomers.

Recent studies have shown that PFOS is one of the most difficult organic pollutants to degrade discovered so far. It has high persistent stability in the environment and can strongly accumulate in the environment, human body, and tissues (with a reported half-life of 8 years in the human body), causing respiratory diseases, producing various toxicities, and even leading to fetal death. Animal experiments have shown that animals can die with 2mg/kg PFOS in their bodies. Therefore, on December 12, 2006, Europe introduced a ban on PFOS, which stipulated that the quality fraction of PFOS in the production raw materials and formulation components cannot exceed 0.005% for products on the European market.

(2) The limit of PFOS in semi-finished products is 0.1%.

(3)The limit of PFOS in textiles and coating materials is 1t~g/m.

The ban was officially implemented on June 27, 2008, marking a comprehensive EU style ban on the use of PFOS in goods. The United States terminated the production and use of PFOS as early as 2001 based on environmental management and human health considerations.

2．2PF0A

Perfluorooctanoic acid, also known as pentafluorooctanoic acid, has the chemical structural formula:

PFOA can also represent ammonium perfluorooctanoate, but it is mainly used in extinguishing foam. PFOA, as a fluorinated surfactant with hydrophobic carbon chain perfluorination, is currently used in textiles both domestically and internationally; Three defenses; The second most important raw material in finishing agents after PFOS, such as used in the manufacture of perfluorooctanol polymers of acrylic acid. Recent studies have shown that the impact of PFOA on the ecological environment and human health is similar to that of PFOS, and it also accumulates strongly in the environment, human and animal tissues. At present, there is still uncertainty about the potential harm of PFOA to the human body, and how it transfers to the environment and causes harm to the human body has not been established and confirmed. The US Environmental Protection Agency (EPA) believes that more scientific data is needed to conduct hazard assessments in order to ban or restrict its use. The EU only mentioned in its ban on PFOS that it suspects PFOA and its salts have similar risks to PFOS, but currently many textile companies and brand textile sellers have accepted the view that PFOA and its salts pose potential risks to human health and the environment based on the WTO's precautionary principle. In the chemical restriction clause, it is explicitly required that textiles should not detect PFOA and its salts. The EPA has also proposed a PFOA voluntary reduction plan (also known as the Stewardsllip Plan), which requires companies in the United States to reduce PFOA emissions by 95% by 2010 and achieve zero emissions by 2015. In fact, many companies in the United States have been independently reducing their emissions. For example, DuPont has recently developed a new fluorine based polymer manufacturing technology (Echelon technology) that can reduce trace PFOA residues by 97%. The LX platform high-performance organic fluorine products have been launched on the market since the first quarter of 2007 and can be used in surface protection fields such as fluorine surfactants, coatings, leather, and paper packaging.

PFOS and PFOA are also produced during the manufacturing or decomposition (chemical or biological degradation) of fluorinated surfactants. Considering that PFOS and PFOA are toxic chemicals with high persistent environmental stability and high bioaccumulation, and have strong environmental migration ability and wide pollution range, the United Nations Environmental Protection Agency has listed them on the United Nations POPs (Persistent Organic Pollutants) list and banned them. Not long ago, in a water quality survey in China, it was found that the content of these two chemicals in rivers was relatively high. For example, in the Huangpu River, PFOS content was detected as 26.46mg/L and PFOA content was 159.83mg/L.

3New alternatives to finishing agents

The development of PFOS and PFOA alternatives can be roughly divided into two stages, with the first stage before 2007 and the second stage thereafter. The preliminary investigation of the first stage shows that several major companies in the market produce fabric multifunctional finishing agents based on new fluorinated surfactants, all of which contain PFOS, but the content of PFOA is relatively low. DuPont in the United States has reduced the residual amount of PFOA in its products by more than 97%, while products from Asahi Glass Corporation in Japan and 3M in the United States generally do not contain PFOA, but are not stable enough. Except for a few companies' products, these new alternatives do not contain APEO. In the second stage, Swiss company Clariant, Japanese company Asahi Glass, and German company Rudolf developed environmentally friendly alternatives to fluorinated surfactants, which are essentially free of PFOS and PFOA (below the detection limit) and have long-lasting finishing effects. In addition, detection methods for ultra-low content PFOS and PFOA have been successfully developed in these two stages. In general, solvent extraction of PFOS or PFOA and analysis using LC/MS method can meet market requirements, but this detection method is not applicable for ultra-low content. SevenRent Laboratory in the United States has developed a new detection method for low levels of PFOA in soil and water, using solid-phase extraction for water and acoustic treatment for soil, followed by analysis using LC/MS/MS. The method can detect PFOA in water at levels of several parts per trillion and in soil at levels of several parts per billion, making it widely applicable and sensitive for environmental testing. It is said that this method can also be used for detecting ultra-low levels of PFOA in products. These new alternatives are mainly developed through the following six approaches.

3．1 PFHS和PFHA

PFHS stands for perfluorohexane sulfonate or sulfonamide, while PFHA stands for perfluorohexanoic acid. Due to the use of new fluorinated polymer manufacturing technology or PFHA in these products, the multifunctional finishing agents produced do not contain PFOA (below the detection limit) and PFOS. Its toxicity is lower than PFOS and PFOA, and its waterproof, oil repellent, and anti fouling properties are similar to PFOA and PFOS. There are five typical varieties.

(1)NuvaN2114liq．

It is a PFOA free (detection limit of 20×); C6 environmentally friendly ultra durable fluorine-containing waterproof and oil repellent finishing agent (less than 10mg/kg) is a weakly cationic white dispersion. AATCC22 Spray, AATCC118 Oil, DINEN29865, Bundes manntest& Tests such as the Water/Alcohol drop test (Isopropanol-1PA) have shown that the properties of the fabric treated with it remain unchanged after multiple washes. It is suitable for cellulose fibers, synthetic fibers, and their blended fabrics, with a wide range of applications. The soaking and rolling process formula for 100% cotton washable indoor decorative fabric is as follows:

Dip rolling process prescription/(g/L)

ArkoifxNDFliq．(Fiber Crosslinking Agent)       50

CatalystNKCliq．(Crosslinking catalyst)     2 5

CerlaubeSVNIP133liq．(Non ionic lubricant/softener)     15

NuvaN2114liq．(C-Fluorochemical)       7O

FluorowetUDliq．(Wetting agent)             5

The pH value of the above-mentioned immersion rolling solution is 4-5, with a rolling rate of 75%. After immersion rolling, it is dried and then baked at 175 ℃ for 30 seconds (residence time).

(2)NuvaN4118liq．

It is a hydrophilic C6 fluorinated easy to clean finishing agent, free of PFOS and PFOA (PFOA detection limit is 20×); 10mg/kg or less), with excellent fine hair wetting effect and good durability, can be combined with Arkoifx resin. This product has similar performance to PFOS or PFOA products.

(3)AsahiguardAG—E061

It is a new type of fluorinated waterproof and oil repellent finishing agent that does not contain PFOA (below the detection limit). It has high water and oil repellency, good durability, and compatibility with other additives. It has the characteristics of rapid processing and low-temperature baking. Additionally, AsahiguardAG— E061 can also be used as an oil resistant processing agent for paper. Japan's Asahi Glass Co., Ltd. has specially designed an E-series product production line based on C6 chemical technology. Guangdong Demi Fine Chemical Co., Ltd. in China has obtained the agency rights for this product, which has already been sold in the domestic market.

(4)UnidyneMultiSeires

It is developed by Daikin Kogyo Co., Ltd. in Japan and does not contain PFOA (with test results in 5×); A new waterproof and oil repellent finishing agent for harmful chemicals such as 10mg/kg or less, PFOS, and APEO, suitable for clothing, paper, and non-woven fabrics.

(5)Fluorine containing waterproof and oil repellent finishing agent

China is researching and developing multifunctional fluorine-containing finishing agents based on C6.

The above new C6 fluorinated waterproof and oil repellent finishing agents have excellent waterproof and oil repellent properties, but their oil repellent performance is slightly inferior compared to PFOS or PFOA products (Table 1).

3．2PFBS

PFBS, also known as perfluorobutane sulfonate or sulfonyl compounds, has no significant persistent bioaccumulation and low toxicity compared to PFOS due to its short fluorocarbon chain. It can be excreted from the body through metabolism and its degradation products are non-toxic and harmless. The new product made of PFBS by 3M Company in the United States has good protective functions and is harmless to the environment and human health. It has been approved by the US EPA and other environmental agencies around the world, and there is a new product called Scotch‐ GuardPM-3622 and PM-3630 have super waterproof function; ScotchugardPM-492 has easy to clean function; Scotchguard PM-930 has anti fouling and easy to clean functions; Scotchguard PM-226 has functions such as moisture absorption and easy cleaning. These new products still have a considerable gap in oil repellency compared to products made with PFOS, even when compared to the oil repellency of C perfluoroalkyl acrylate (Table 1).

3．3Nano fluorinated finishing agent

The nano fluorinated multifunctional finishing agent manufactured using nanotechnology achieves waterproof and oil repellent effects by reducing the surface energy of fabrics and creating a rough surface with nano microstructures. This type of finishing agent is also known as nano hybrid fluorinated waterproof and oil repellent finishing agent. The finished fabric not only has good waterproof and oil repellent properties, but also can maintain the characteristics of nano products well. Typical varieties include:

Rucostar series

They are environmentally friendly fluorinated three proof finishing agents developed by Rudolf based on biomimetic and nanotechnology, with the main variety being RucostarEEE. It achieves waterproof, oil repellent, and stain resistant effects through the self discharge of special additives (fluorocarbon polymers) and dendritic polymers in the nanometer range, and then co crystallization. Similar varieties include RucostarEEN and EEW, both of which are suitable for the three proof finishing of all fiber fabrics. This series of products has a low fluorine content and does not contain APEO or PFOS. The PFOA content does not exceed 1mg/kg. In addition, the company has also developed a fluorine free series of waterproofing agents using the same technology, namely the Ruco Dry series, with the main variety being Ruco— DryDHT。 It utilizes the self draining ability of dendritic polymers to form nanoscale crystalline structures on textiles, with excellent waterproof, washable, and wear-resistant properties. It does not require a high temperature (around 140 ℃) during sorting, and does not contain APEO, PFOS, or PFOA, making it suitable for waterproof finishing of sports and outdoor textiles.

3. 4Compound fluorinated finishing agent

The critical surface tension of general hydrocarbon surfactants, siloxane surfactants, polyacrylate hydrocarbons, etc. in water is sometimes higher or lower than that of fluorocarbon surfactants (Table 3). Although their performance is inferior to that of fluorinated hydrocarbon surfactants (Table 4), according to the principle of additive enhancement, they are combined with fluorinated hydrocarbon surfactants for oil repellency according to AATCC118— Determination of 20o2 "Oil repellency and hydrocarbon resistance test". By compounding to manufacture multifunctional finishing agents, the applicability of fluorinated surfactants can be improved.

The use of compounding technology can not only reduce the dosage and cost of fluorinated surfactants to enhance their effectiveness, but also lower the content of PFOS and PFOA in the final product below the limit value. For example, combining fluorine-containing waterproof and oil repellent finishing agents with pyridine based waterproof agents not only does not affect the oil repellent effect, but also improves the waterproof and wash resistance of fabrics with less PFOS or PFOA content. For example, by compounding fluorine-containing waterproof and oil repellent finishing agents with hydroxymelamine derivative waterproof agents, not only does the waterproofing performance improve, but the oil repellent performance also increases by 1-2 levels. It is reported that Umd~eTG.5521 from Etben Daikin Industries is also a compound fluorine-containing finishing agent, which can achieve durable waterproof and oil repellent effects when used for textile finishing, and has a soft hand feel.

3. 5Fluoroalkyl acrylate resin

At present, most fluorine-containing waterproof, oil repellent, and anti fouling finishing agents are acrylic or methacrylate polymers, and the differences between the finishing agents mainly lie in the connecting groups between the fluorinated alkyl group and the polymer main chain. PFOS is a fluorinated surfactant connected by sulfonamide groups, with the following structure:

If the sulfonamide group is removed, it becomes CnF_2n+1CH2CH2COCH— CH structure, which is the fluorinated acrylic ester resin. So far, there have been no reports of its harm to the ecological environment and human health, and its waterproof, oil repellent, and stain resistant properties are similar to those of multifunctional finishing agents based on PFOS. Typical products include Asahiguard AG-480, and corresponding products are available from companies such as 3M, DuPont, and Daikin Industries. Their waterproof and oil repellent properties are related to the length of the carbon chain, and acrylic esters can be used as comonomers for copolymerization. Most finishing agents are made into water lotion for use. The commonly used emulsifiers are fatty acid polyoxyethylene ether or a mixture of several surfactants, and APEO is no longer used; If it is made into a solvent type, organic solvents such as vinyl chloride can be used.

3. 6Polytetrafluoroethylene

Polytetrafluoroethylene water lotion with a certain degree of polymerization is used to set the textile at 160~165 ℃ for 30s. The polymer conjunctiva is formed. The contact angle between this film and water is 108^o~114^o. The contact angle with oil is also large, and the washing resistance is good, indicating that the polytetrafluoroethylene has

Good waterproof and oil repellent function, suitable for the requirements of multifunctional textile finishing.

3. 7Other

Atofina Chemical Company and Dow Corning Corporation in the United States, Hill Corporation in Germany, Mitsui Chemicals Co., Ltd. and Dow Toray Siloxanes Co., Ltd. in Japan, as well as the Institute of Chemistry of the Chinese Academy of Sciences and Wuhan University in China, have all conducted research in this area and applied for patents. For example, China has synthesized a fluorine-containing silicone finishing agent, mainly composed of fluorinated acrylic acid esters, fluorinated methyl methacrylate esters and their mixtures, long-chain alkyl acrylate esters, or long-chain alkyl methyl methacrylate esters and their mixtures grafted modified with methyl hydrogenated silicone oil, which can endow textiles with waterproof, oil repellent, soft and breathable functions, and is affordable. Suzhou University has recently developed a new type of octafluoropentethoxypropyl methyl silicone oil finishing agent, which combines the advantages of organic fluorine and organic silicon, and has good comprehensive performance. It is a good development direction for silicone fluorine waterproof and oil repellent finishing agents.

4Conclusion

Due to the best combined effect of PFOS and PFOA among fluorinated surfactants, they have been widely used in many fields. However, extensive research has confirmed that these two substances are currently one of the most difficult organic pollutants to degrade in the world, with persistent environmental stability, high bioaccumulation, and strong environmental migration ability. The United Nations will include them in the POPs list for prohibition. From the current alternatives, the finishing agent produced by the new C6 fluorinated surfactant has the best substitutability, but there are still issues such as economy and overall functionality. Accelerating the development of new low toxicity or non-toxic durable alternatives that are environmentally friendly, ecologically harmless, and safe for human health remains an important task at present.