Understanding surfactants in your laundry detergent

When it comes to keeping your clean cloth nappies and laundry truly clean, the detergent you choose plays a crucial role. One of the most important ingredients in any effective laundry detergent is a class of compounds called surfactants. You might not have heard the term before, but these powerful little molecules are working hard behind the scenes to lift away mess and leave your nappies fresh and clean.

The component of the detergent that is most important in creating bubbles are surfactants (meaning ‘surface agent’). Surfactants stir up activity on the surface you are cleaning to help trap dirt and remove it from the surface.

International Products Corporation

How surfactants work

The word ‘surfactant’ is a shortened form of ‘surface-active agent.’ This name gives us a big clue about what they do: they reduce the surface tension of water. Imagine water molecules clinging tightly to each other – that’s surface tension. When you add surfactants, they break up these tight bonds, allowing the water to spread out and penetrate fabrics more easily.

But their real superpower lies in their unique molecular structure. Surfactant molecules have two distinct ends:

• A ‘hydrophilic’ (water-loving) head: This part is attracted to water.
• A ‘hydrophobic’ (water-fearing or oil-loving) tail: This part is repelled by water but attracted to oils, greases, and dirt.

This dual nature is what makes them so effective at cleaning. When you wash your nappies, the hydrophobic tails of the surfactant molecules attach themselves to the dirt, oils, and general grime on the fabric. At the same time, the hydrophilic heads are attracted to the water in your wash.

As the washing machine agitates, the surfactant molecules surround the dirt, lifting it away from the fabric and suspending it in the wash water. They essentially form tiny micelles around the dirt particles, preventing them from redepositing back onto your clean nappies.

Matching detergent to your soiling level

It is important to adjust your detergent to the amount of soiling in the wash. If there is more soiling than surfactants, all the soiling cannot be bound and removed by the cleaning agents. This means some soiling is left behind.

Detergents packaging typically list different doses for larger and heavily soiled loads. However, these doses are based on assumptions about the size of your washing machine/ load, amount of soiling and water hardness (as minerals in hard water can also bind to surfactants, leaving them unavailable to clean the washing). 

Each wash cycle is different, the level of soiling is never identical. You might have the same cycle length and water temperature but the the soiling and staining of each load is different. This means you need to be mindful of when to adjust the detergent dose (and chemical factors).

~ Anastasia, Environmental Scientist and founding Facebook group admin

It’s essential to note that our detergent dosage calculator takes these water hardness and machine size into account, but it still makes assumptions about the level of soiling. Aim to see suds one third (⅓) of the way through the main wash cycle. This confirms that there is a small excess of surfactants and that soiling won’t be left behind because of under-dosing.

The downside of traditional soaps

While the term ‘soap’ is sometimes used interchangeably with ‘detergent,’ traditional soaps (made from fats and lye) work differently from modern detergents.

Unlike surfactants that keep dirt and themselves suspended and easily rinsed away, traditional soap can cling to the fabric itself. With repeated washes, any undissolved soap particles accumulate layer by layer on the fabric. This build-up creates the sticky, waxy, and often grayish residue known as ‘scrud’ or ‘soap scum’.

When it comes to cloth nappies, this leads to:

• Reduced Absorbency: The greasy, waxy layer of scrud coats the fibres, preventing them from effectively soaking up liquid. This can lead to leaks and a false impression that your nappies are ‘repelling.’
• Stiffness and Roughness: The build-up makes the fabric stiff and rough to the touch, which can be uncomfortable for your baby.
• A ‘waxy’ coating on the inside of your washing machine drum or door seals.
• Odour Issues: Scrud can trap bacteria and dirt, leading to persistent ammonia smells or barnyard smells, even after washing.
• Skin Irritation: The residue can be irritating to your baby’s sensitive skin, causing rashes.

Thankfully, the surfactants used in high-quality, modern laundry detergents are specifically formulated to be clean rinsing. This means that once they’ve done their job of lifting and suspending dirt, they are easily washed away with the rinse water. They don’t cling to the fabric, ensuring that your cloth nappies come out of the wash genuinely clean, free from detergent residue, and ready to absorb efficiently.