###### Abstract  
In this study, the effect of the hydrophilic-lipophilic balance (HLB) number and cloud point (CP) of a secondary-alcohol ethoxylated nonionic surfactant on degenerasing efficiency was investigated. A degreasing process was conducted for steel samples with different surfactants in a degreasing solution. The HLB number and CP increased with the increasing \(n\) of the hydrophilic ethylene oxide (OCH\({}_{2}\)CH\({}_{2}\))\({}_{n}\) group. For a constant temperature of the degreasing solution (30-80 \({}^{\circ}\)C), the degreasing efficiency was investigated as a function of degreasing time. The highest degreasing efficiency was observed near the cloud point of the surfactant, and the degreasing efficiency decreased significantly at temperatures lower and greater than the cloud point. A Hogaboom test was carried out to observe oil stains on the surface of samples. Additionally, the contact angle of the surface with water droplets was measured after degreasing with various surfactants. degreasing; HLB; pre-treatment process; nonionic surfactant; cloud point +
Footnote †: journal: Applied Sciences  
location of solubilization is determined by the molecular structure of the solubilizer and solubilize, and the hydrophilic-lipophilic balance (HLB) number. The factors influencing solubilization include chemical structure effects of the surfactant, such as the alkyl group length, functional group type and position, ionic effect, HLB number, solubilize effects, concentration, temperature, and additives [4; 5; 6]. Atlas, a surfactant manufacturer in the 1950s, first used the HLB as an indicator to represent the properties of nonionic surfactants. Based on the work conducted by [PERSON], [PERSON] proposed an equation to express the HLB number as a function of the weight fraction of a hydrophilic group of a nonionic surfactant (Equation (1)) and claimed that the optimal condition for oil emulsification corresponds to the weight fraction of a hydrophilic group in the emulsifying agent molecule. Several methods have since been proposed to calculate the HLB from the chemical structure of an emulsifying agent [7; 8; 9]; however, the equations are all based on the proportion of hydrophilic groups that constitute the molecules of an emulsifying agent as below. \[HLB\;number=20\;\left(1-\frac{M_{0}}{M}\right) \tag{1}\]  
where \(M_{0}\) is the molecular weight of the hydrophobic portion and \(M\) is the total molecular weight [10]. The aqueous solubility of the emulsifying agent increases with the increasing HLB, which increases the critical micelle concentration (CMC) value, i.e., the number of dissolved surfactants outside micelles increases as well. Conversely, a decrease in the HLB number induces the opposite effect. Since the introduction of the concept by [PERSON], the HLB has been widely used to select emulsifying agents. However, the strong influence of temperature must be considered [10; 11; 12; 13; 14; 15; 16]. One other critical factor affecting degreasing efficiency is cloud point, which refers to the temperature transforming an isotropic micellar state into a two-phase state of surfactant solution. The cloud point of an alcohol ethoxylate is influenced by HLB, the number of ethylene oxide, and hydration state [17]. Many studies of the HLB of surfactants have been actively conducted in the pharmaceutical, paint, cosmetic, and food industries, but no research on HLB is sufficient in the electroplating field, especially for the pre-treatment process. Meanwhile, to the best of our knowledge, there has been no study focused on the influence of cloud point on degreasing efficiency. In this study, the effect of the HLB number and cloud point (CP) of secondary alcohol ethoxylate nonionic surfactant (Equation (2), where R, R1, R2, R3, and R represent the alkyl group of RCOOR\({}^{\prime}\)) on its degreasing performance was evaluated.