Soil redeposition

What is soil redeposition?

Cleaning happens in stages. Surfactants and other ingredients loosen soil from a surface and bring it into the wash water, but the job is only complete if that soil stays in the water until it drains away. When removed particles or oily soils settle back onto the clean fabric or surface, the result is redeposition. In laundry, it shows up as gradual graying or yellowing of whites and dulling of colors over many washes.

Causes

• Too little detergent for the soil load, so there is not enough to keep soil suspended.
• Hard water, which reduces surfactant effectiveness and can bridge between soil and fabric.
• Overloaded machines and short rinse cycles.
• Fabric type. Synthetic fibers can attract oily soils.

How detergents prevent redeposition

• Antiredeposition agents, such as sodium carboxymethyl cellulose and polycarboxylate polymers, which adsorb onto fibers and soil particles and keep them apart.
• Dispersants and surfactants that suspend particles and emulsify oily soil.
• Detergent builders, which soften the water and often increase the negative charge on soil and fiber surfaces so they repel each other.
• Soil release polymers, which make fabrics easier to clean in later washes.

Preventing redeposition is part of overall detergency.

Note on the acronym CMC

In detergents, CMC usually means carboxymethyl cellulose, an antiredeposition agent. In surfactant science, CMC means critical micelle concentration. The two are unrelated.

Frequently asked questions