1. Relationship Between Names and Physical Forms

In the selection and production use of raw materials for household and personal care products, names such as sodium hydroxide flakes, granular sodium hydroxide, caustic soda, lye, and caustic alkali often appear together. Caustic soda, lye, and caustic alkali usually refer to sodium hydroxide, with the chemical formula NaOH. Sodium hydroxide flakes and granular sodium hydroxide are different commercial forms of solid sodium hydroxide. Their differences are mainly reflected in appearance, feeding method, dissolution behavior, storage, and ease of use.

In household and personal care product manufacturing, the key question is whether a particular form of sodium hydroxide is suitable for the formulation requirements, feeding method, dissolution conditions, storage conditions, and safety management requirements of the product being produced.

2. The Fundamental Role of Sodium Hydroxide in Household and Personal Care Products: Strong Alkalinity and Hydroxide Ions Are the Key

Whether sodium hydroxide flakes, granular sodium hydroxide, or liquid caustic soda is used, once sodium hydroxide enters an aqueous system, it provides Na⁺, sodium ions, and OH⁻, hydroxide ions. In pH adjustment, neutralization reactions, and saponification reactions, the key effect mainly comes from the strongly alkaline environment provided by OH⁻. This is the fundamental reason why sodium hydroxide can play an important role in household and personal care product manufacturing.

2.1 Increasing System pH and Adjusting Product Acidity or Alkalinity

pH, an indicator of acidity and alkalinity, affects the stability, irritation potential, cleaning power, thickening performance, and raw material compatibility of household and personal care products. Sodium hydroxide can significantly increase the pH of an aqueous system, so it is commonly used for pH adjustment in formulations. In actual formulations, changes in pH may affect the salt form of surfactants, the state of thickeners, the effectiveness of preservation systems, product appearance, and safety during skin contact. Therefore, the dosage, concentration, and method of addition of sodium hydroxide all need to be precisely controlled.

For personal care and cleansing products used close to the human body, sodium hydroxide is usually used only as a low-level pH adjuster. For highly alkaline products such as heavy-duty degreasers and drain cleaners, sodium hydroxide may become an important component that determines cleaning performance as well as corrosion risk.

2.2 Neutralizing Acidic Raw Materials and Changing System Structure and Performance

Fatty acids, acidic surfactants, or other acidic raw materials are often used in household and personal care formulations. Sodium hydroxide can react with these acidic substances through neutralization to form the corresponding sodium salts.

This process is not merely a change in pH. It can also affect the solubility, viscosity, transparency, foaming behavior, and storage stability of the system. For example, fatty acids can form sodium fatty acid salts after neutralization with sodium hydroxide. Some acidic surfactants must be neutralized before they can form sodium salt surfactants suitable for formulation use.

2.3 Participating in Saponification Reactions to Form Soap-Based Cleaning Components

In soap, soap base, and certain cleaning products, an important role of sodium hydroxide is to promote the saponification of oils and fats. Triglycerides in oils and fats are hydrolyzed under strongly alkaline conditions to form glycerol and sodium fatty acid salts. Sodium fatty acid salts are an important source of soap-based cleaning components.

In saponification reactions, the decisive factors include the effective NaOH content entering the reaction system, the concentration of the alkaline solution, the uniformity of alkali addition, and temperature control. If the effective alkali amount is insufficient, saponification of oils and fats may be incomplete. If the alkali amount is excessive, the free alkali level may become too high, increasing product irritation and safety risks.

2.4 Enhancing Degreasing Ability While Increasing Corrosion and Irritation Risks

In strongly alkaline cleaning products, sodium hydroxide can help hydrolyze, saponify, disperse, and detach oily soils, thereby improving the removal of heavy grease, deposits, and certain organic soils. However, strong alkalinity does not mean suitability for all household and personal care products. The higher the alkalinity, the greater the potential risk to skin, eyes, metals, coatings, fabrics, and certain plastic materials. Sodium hydroxide may also react with metals such as aluminum and zinc, creating corrosion and safety hazards.

When sodium hydroxide is used in cleaning products, cleaning power should not be the only consideration. Material compatibility, corrosion control, packaging suitability, labeling warnings, and the actual method of use must also be considered.

3. Why Use Performance Differs Even When Chemical Properties Are Basically the Same

If sodium hydroxide flakes and granular sodium hydroxide have similar main components, effective content, and impurity levels, their chemical properties are basically the same. Both are strongly alkaline, strongly corrosive, hygroscopic, capable of absorbing carbon dioxide from the air, and both release significant heat when dissolved in water. Their differences in use mainly come from the influence of physical form on dissolution, feeding, storage, and safe handling.

3.1 Physical Form Affects Dissolution Behavior

Sodium hydroxide flakes are usually flake-like or thin-flake solids, while granular sodium hydroxide is usually granular or bead-like. Different physical forms affect how the material comes into contact with water, thereby influencing dissolution rate, wetting uniformity, and localized heat release. Sodium hydroxide releases a large amount of heat when dissolved in water. If it is added too quickly all at once, localized temperature rise, solution splashing, excessively high local concentration, or material agglomeration may occur. Both flake and granular forms carry this risk, but the way the risk appears may differ.

3.2 Physical Form Affects Feeding and Metering

In household and personal care product manufacturing, feeding stability directly affects batch-to-batch consistency. Granular sodium hydroxide usually has better flowability and is more convenient for small-batch weighing, laboratory trials, pilot-scale formulation adjustment, and automated feeding when compatible with equipment conditions. Sodium hydroxide flakes are common in bulk use, and procurement and storage systems are relatively mature. However, if they absorb moisture and cake, weighing accuracy and feeding continuity may be affected.

3.3 Hygroscopicity and Carbon Dioxide Absorption Affect Effective Alkali Content

Sodium hydroxide is highly hygroscopic and readily absorbs moisture from the air, leading to deliquescence. At the same time, it also absorbs CO₂, carbon dioxide, from the air and gradually converts into sodium carbonate and other carbonate substances. This creates two practical effects:

① The material’s appearance and flowability deteriorate, resulting in caking, deliquescence, and weighing difficulty.

② The effective NaOH content decreases, causing the actual feeding amount to deviate from the formulation design.

For ordinary cleaning applications, a slight change in effective alkali content may show up as fluctuation in cleaning performance. However, for saponification, neutralization, and precise pH control, changes in effective alkali content directly affect calculation results. If the original labeled content is still used for dosing, insufficient neutralization, incomplete saponification, excessive free alkali, or final pH deviation may occur.

3.4 Physical Form Affects How Safety Risks Appear

Sodium hydroxide flakes, granular sodium hydroxide, and liquid caustic soda are all strongly corrosive. Different forms have different risk priorities. Safety management should be designed according to the material form, and localized high concentration and localized high temperature should be controlled according to the feeding method.

4. Selection Priorities Differ Across Household and Personal Care Applications

4.1 Soap and Soap Base: Focus on Effective Alkali Amount and Reaction Control

In soap and soap base production, the core function of sodium hydroxide is to saponify oils and fats. At this stage, the most important factor is whether the effective NaOH actually participating in the reaction is accurate.

Both sodium hydroxide flakes and granular sodium hydroxide can be used for saponification. For small-scale trials and fine formulation adjustments, granular sodium hydroxide is more convenient to weigh. For large-scale production, sodium hydroxide flakes or liquid caustic soda may have advantages in cost and supply. When solid alkali such as flakes or granules is used, it is recommended to first prepare an alkali solution with a clearly defined concentration and complete dissolution before introducing it into the reaction system. If liquid caustic soda is used, the effective NaOH feeding amount should be calculated based on its actual mass fraction and density.

4.2 Neutralization of Acidic Raw Materials: Focus on Endpoint Control and System Stability

In detergent, cleaning product, and certain surfactant systems, sodium hydroxide is often used to neutralize fatty acids, acidic surfactants, or other acidic raw materials. Neutralization reactions can affect: ① final pH; ② surfactant salt form; ③ solubility and transparency; ④ system viscosity; ⑤ product mildness; and ⑥ long-term storage stability.

In these applications, when choosing sodium hydroxide flakes, granular sodium hydroxide, or liquid caustic soda, priority should be given to whether addition can be controlled. For systems that require precise pH control and neutralization endpoint control, it is generally not advisable to add solid alkali directly into the main system. A pre-prepared NaOH solution with a clearly defined concentration is more suitable. This reduces system fluctuations caused by localized high alkalinity.

4.3 Heavy-Duty Degreasing: Focus on the Balance Between Cleaning Power and Corrosiveness

In heavy-duty degreasing, industrial cleaning, and drain-unblocking products, sodium hydroxide is often used to provide a strongly alkaline environment and enhance the treatment of oily soils.

The selection principle in heavy-duty degreasing applications is to determine an appropriate alkalinity level based on the target soil, the object being cleaned, material compatibility, and safety requirements, rather than simply pursuing a higher NaOH dosage.

4.4 pH Adjustment: Focus on Low Dosage and Controlled Addition

In some household and personal care formulations, sodium hydroxide is not the main functional ingredient but is used to fine-tune pH. The dosage may be small, but its impact on product stability and safety can be significant. In such cases, it is not advisable to add small amounts of sodium hydroxide flakes or granular sodium hydroxide directly into the main system. A safer approach is to first prepare a NaOH solution at a certain concentration, then add it gradually while monitoring pH.

Because solid alkali can create very high local concentrations after entering the system, it may easily cause localized thickening abnormalities, raw material degradation, color changes, or system non-uniformity. For products used close to the skin, pH control is especially important, and rough or uncontrolled dosing should be avoided.

5. How to Choose Between Sodium Hydroxide Flakes, Granular Sodium Hydroxide, and Liquid Caustic Soda

5.1 First Consider Effective Content and Quality Specifications

The effective NaOH content should be confirmed first. Solid sodium hydroxide is usually labeled with different content grades, while liquid caustic soda is labeled with the mass fraction of the solution. If the content differs, the actual feeding amount needs to be recalculated.

During selection, the following should be confirmed as priorities: ① labeled NaOH content; ② product standard or quality specification; ③ control of impurities such as sodium carbonate, chloride, and iron; ④ packaging and sealing condition; ⑤ storage time and moisture exposure; and ⑥ whether the product meets the quality requirements of the target product.

For saponification, neutralization, and precise pH adjustment, dosing should not be based only on the commercial product weight. Instead, it should be calculated based on the effective NaOH content. Otherwise, the actual alkali amount in the formulation will deviate from the design value.

5.2 Then Consider Production Scale and Feeding Method

Different production scales require different suitable forms of sodium hydroxide.

If an enterprise has storage tanks, metering pumps, and pipeline systems, liquid caustic soda is more conducive to automated control in continuous production. If the site mainly relies on manual weighing and batch feeding, sodium hydroxide flakes and granular sodium hydroxide remain commonly used, but moisture control, weighing, dissolution, and temperature control must be strengthened.

5.3 Consider Dissolution and Temperature Control Conditions

Sodium hydroxide releases significant heat when dissolved in water, which is one of the important operational risks when using solid alkali. When preparing an alkali solution, the following points should be controlled:

① Slowly add sodium hydroxide into water.

② Avoid pouring a small amount of water onto a large amount of solid alkali.

③ Maintain agitation during addition.

④ Add in portions when necessary and control the temperature.

⑤ Avoid rapid dissolution in a closed container.

⑥ Use containers and tools resistant to strong alkali corrosion.

If the site lacks good agitation and temperature control conditions, direct use of solid alkali carries a higher risk. In such cases, the amount prepared per batch should be reduced, or a liquid caustic soda solution with stable concentration should be used. If the temperature rises significantly during preparation, the alkali should be added in portions and cooling measures should be taken. The solution should be used for subsequent feeding only after both temperature and dissolution state have stabilized.

5.4 Consider the Final Product Application

The final product application determines the key control points for sodium hydroxide.

6. Common Misconceptions

6.1 Misconception 1: Granular Sodium Hydroxide Has Stronger Chemical Performance Than Sodium Hydroxide Flakes

This is inaccurate. The main difference between granular sodium hydroxide and sodium hydroxide flakes is physical form, not chemical reactivity. If the NaOH content and impurity levels are similar, the strong alkalinity they provide after dissolution is basically the same. Granular sodium hydroxide is often more convenient to use because of its flowability, weighing behavior, and feeding performance, not because its alkalinity is inherently stronger.

6.2 Misconception 2: Caustic Soda, Sodium Hydroxide Flakes, and Granular Sodium Hydroxide Are Three Different Chemicals

This is inaccurate. Caustic soda is usually a common name for sodium hydroxide, while sodium hydroxide flakes and granular sodium hydroxide are commercial forms of sodium hydroxide.

6.3 Misconception 3: The Stronger the Alkalinity, the Better the Cleaning Effect

This is not entirely correct. Increasing alkalinity can usually enhance the treatment of oily soils, but it also increases the risk of corrosion, irritation, and material damage. The performance of a cleaning product is not determined by NaOH alone. It is also related to surfactants, solvents, chelating agents, corrosion inhibitors, use concentration, contact time, and the object being cleaned. High alkalinity is one cleaning approach, but it is not the best choice for every cleaning scenario.

6.4 Misconception 4: As Long as They Are All NaOH, They Can Be Directly Substituted

Direct substitution is not recommended. When sodium hydroxide flakes, granular sodium hydroxide, and liquid caustic soda are substituted for one another, the effective NaOH content should at least be recalculated, and dissolution method, feeding rate, system water content, temperature change, and safety measures should be evaluated. When solid alkali is replaced with liquid caustic soda, the water content in the formulation changes. When liquid caustic soda is replaced with solid alkali, dissolution heat release and localized high-concentration risks increase. These changes may affect production stability.

7. Classification of Representative Chemicals Related to the Selection of Sodium Hydroxide Flakes, Granular Sodium Hydroxide, and Caustic Soda in Household and Personal Care Product Manufacturing

Note: The following tables provide examples of representative reagents and related products for scientific research, small-scale trials, formulation research, and quality control scenarios. For actual production feeding, further confirmation should be made based on product regulations, quality standards, COA, SDS, and internal validation results.

Table 1. Core Strong Alkali Raw Materials and Sodium Hydroxide Specifications

Table 2. Alkaline Additives, Inorganic Builders, and Supporting Raw Materials for Cleaning Systems

Table 3. Saponification Raw Materials and Surfactant-Related Products

Table 4. Supporting Products for Acid-Base Adjustment, Chelation, Buffering, and Titration Testing

Note: The above products are representative Aladdin products related to scientific research and formulation studies. For more product specifications, grades, and COA information, please search by product name, CAS number, or catalog number on the Aladdin official website.

References

[1] National Center for Biotechnology Information. PubChem Compound Summary for Sodium Hydroxide.

[2] National Institute for Occupational Safety and Health. NIOSH Pocket Guide to Chemical Hazards: Sodium Hydroxide.

[3] European Chemicals Agency. Sodium hydroxide: Substance Infocard and registration information.

[4] International Labour Organization and World Health Organization. International Chemical Safety Card ICSC 0360: Sodium hydroxide.

[5] GB/T 209—2018, Sodium Hydroxide for Industrial Use.

[6] Kirk-Othmer Encyclopedia of Chemical Technology. Sodium Hydroxide.

[7] Ullmann’s Encyclopedia of Industrial Chemistry. Sodium Hydroxide.

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