Development Trend of Surfactants for Metal Cleaning

Metal cleaning is an indispensable process in the metal processing process, such as cutting, electroplating, painting and other processes must be cleaned before the workpiece to remove rust, oil, scale, dust and so on. Metal cleaning agents can be generally divided into solvent and water based two categories, solvent based cleaning agents have petroleum solvents and halogenated hydrocarbon solvents, because the former has many problems, such as flammable, polluting the environment, waste of energy, so that their application is greatly limited, in many occasions has been gradually replaced by water based cleaning agents. Water-based cleaning agent has become the main development direction of metal cleaning industry.

The water-based cleaning agent is a mixed system composed of surfactants as the main active components and supplemented by other auxiliaries. Surfactants have a great impact on the cleaning process, such as: (1) Surfactants can destroy the bond between the metal surface and dirt; ② Can wet the metal surface, so that the cleaning liquid can surround the dirt particles; (3) It can emulsify animal and plant oils into small droplets and disperse in the solution; ④ can dissolve solid dirt particles; ⑤ Can disperse all kinds of dirt to prevent redeposition. Changing the chemical composition of the surfactant will alter its ability to act at each stage of the cleaning process. Surfactants used as cleaning agents can disrupt the interaction between dirt particles and metal surfaces, but the wetting, penetration, and emulsification capabilities of these surfactants may not be good enough, so several different surfactants are often included in the formulation of water-based cleaning agents. The choice of surfactant is also related to the cleaning process. For example, low-foam cleaning agent is needed in the spray washing process; In ultrasonic cleaning, it is necessary to use a cleaning agent with good redeposition resistance; In the pipeline cleaning, it is necessary to use high emulsification and high wettability cleaning agents.

Metal surfaces cleaned with water-based cleaning agents often adsorb a layer of surfactant molecules, which can affect the next process, especially for oxygen system components there is a risk of fire. Therefore, the cleaned metal parts must be rinsed with a large amount of deionized water to remove the adsorbed surfactants. For the cleaning of oxygen supply system components, it is best to use surfactants that are easily desorbed.

The use of a large number of water-based cleaning agents, wastewater treatment has also become a serious problem. In the past, we focused on the cleaning performance and service life of the cleaning agent, but now the formulation of spray or ultrasonic cleaning agents is completely different from the past. It is not best to fully emulsify the organic dirt into a component of the cleaning solution. Instead, it is hoped that after stirring stops or cooling, the organic dirt can be released from the emulsion, so that when the grease or dirt is separated, the cleaning agent can be regenerated. Cleaning agents and dirt can be separated using membrane filtration technology, which separates molecules based on their size, shape and charge.

In recent years, the characteristics of microemulsion have also attracted people's attention. Microemulsions exist in the phase region of a multicomponent system composed of water, oil, surfactants, auxiliary surfactants and electrolytes, and have ultra-low interfacial tension and high solubilization ability to hydrophilic and lipophilic substances. Therefore, microemulsion as a medium in fabric decontamination can combine the solubilization of organic solvents with traditional wet washing properties. Raney et al. have used a typical water/surfactant/cosurfactant/electrolyte multicomponent system for standard decontamination tests. They believe that if a microemulsion is formed between the cleaning medium and the oil in the washing process and the washing temperature is close to the phase transfer temperature of the microemulsion, the detergency of the system reaches the maximum.