The type of desiccant can be determined through two core dimensions: its composition and its purpose. The composition determines its moisture absorption principle (chemical or physical), while the purpose reflects its applicable scenarios and safety. Here are the specific methods for determination:
Determining the type of desiccant by composition
Chemical desiccants (absorb water through chemical reactions)
Calcium oxide (quicklime, CaO)
Characteristics: White lumps or powder; reacts violently with water and releases heat, producing calcium hydroxide.
Identification criteria: Packaging indicates "Do not come into contact with water" and "Prevent burns." Commonly found in food packaging such as rice crackers and seaweed.
Caution: Due to its strong alkalinity, accidental ingestion may burn the digestive tract. It has been gradually replaced in food packaging in recent years.
Calcium chloride (CaCl₂)
Characteristics: White porous granules; deliquesces into a liquid after absorbing moisture; the moisture absorption rate can reach 300% of its own weight. **Identification Criteria: Commonly used in containers, large warehouses, or dehumidifier boxes; liquid accumulates at the bottom after absorbing moisture.
Safety: Food-grade calcium chloride can be used for moisture protection of dried goods such as nuts, but high-concentration solutions may irritate the skin.
Calcium Sulfate (CaSO₄)
Characteristics: Processed from natural gypsum, with a moisture absorption rate of approximately 20%–30%, and is inexpensive.
Identification Criteria: Primarily used for moisture protection in industrial applications such as instruments and electrical appliances; less common in everyday consumer goods.
Physical Desiccants (Adsorbing Moisture Through Porous Structures)
Silica Gel (SiO₂)
Characteristics: Transparent or colored spheres; chemically stable, non-toxic, odorless, and reusable.
Identification Criteria: Commonly found in pharmaceuticals, electronic products, and food packaging (such as xylitol); some have a color-changing indicator (turns from blue to red after absorbing moisture).
Advantages: Recognized by the EU as the only type of desiccant suitable for food use.
Montmorillonite (Bentonite)
Characteristics: Grayish-white or pale yellow granules, made from natural minerals, environmentally friendly and non-toxic.
Identification Criteria: Primarily used in precision instruments, optical equipment, food packaging, and other applications requiring high safety.
Fiber Desiccant
Characteristics: Made from plant fibers or starch-based materials, biodegradable.
Identification Criteria: Used in environmentally friendly food packaging; gradually hardens after absorbing moisture, but its efficiency is lower than silica gel.