Why are builders such as sodium carbonate added to laundry detergents?

Builders such as sodium carbonate (soda ash) are added to laundry detergents primarily to increase their detergent action and cleaning efficiency.1

These alkaline materials serve several key functions:

• Water Softening: Builders help manage hard water, which contains dissolved calcium and magnesium minerals. Sodium carbonate acts as a water softener by precipitating these minerals out of the solution, preventing them from interfering with the cleaning process.2
• Enhanced Cleaning: By neutralizing the effects of mineral ions, builders ensure that the detergent can effectively dislodge foreign matter from fabrics and keep it in suspension, rather than allowing it to redeposit on the clothes.13
• Alkalinity: As an alkaline salt, sodium carbonate helps maintain the pH levels necessary for effective soil removal during the wash cycle.14

While phosphates were historically used as highly effective builders, their use has been largely restricted or banned in many countries due to their role in contributing to wastewater pollution and the overgrowth of algae in aquatic ecosystems.1