Laundry detergent: powder or liquid?

Choosing a laundry detergent can feel overwhelming because there are so many options. Most products will make your washing cleaner to some extent, but which one delivers the best result for both your clothes and your budget?

Are you aiming for whiter whites? Are enzymes necessary? And how does powder detergent differ from liquid detergent?

As with many everyday choices, a basic understanding of the chemistry can help answer these questions.

What is a detergent?

The cleaning ingredients in both laundry powder and laundry liquid are surfactants, which are also called detergents – hence the name of the products. These are generally charged, or 'ionic', molecules with two separate structural sections. One section interacts readily with water, while the other is attracted to oils.

Because of this property, surfactants can remove grease and dirt from textiles, holding them suspended in the wash water. They are also able to create bubbles.

Dissolved metal salts in the water supply can reduce how effectively surfactants work. Hard water, for example, contains substantial amounts of dissolved calcium and magnesium salts, which can easily produce soap scum.

For this reason, contemporary laundry detergents include phosphates, water softeners and other metal 'sequestrants' that prevent soap scum from developing. Since phosphates may trigger algal blooms in freshwater ecosystems, modern formulations use them in lower quantities.

Optical brighteners are included in many detergents as well. By absorbing ultraviolet light and emitting blue light, these chemicals create the effect described as “whiter white” or “brighter colour”.

Fragrances are also commonly present in laundry detergents. Although they have no essential role in the cleaning chemistry, they make clothes seem fresh.

Finally, certain laundry detergents include enzymes – discussed further below.

What's in laundry powder?

Although detergents and anti-scum ingredients are the key components, they are not present in the greatest quantity. Powders mainly consist of salts, such as sodium sulphate, which provide bulk and prevent the product from forming clumps.

Sodium carbonate, better known as washing soda, is another salt frequently included in laundry powders. Washing soda, which is chemically related to baking soda, alters grease and grime so that they can dissolve in water.

Powder detergents often also use oxidising substances such as sodium percarbonate. This is a stable blend of washing soda and hydrogen peroxide. Tetraacetylethylenediamine, an added ingredient, activates percarbonate to produce a gentle bleaching action.

From a chemical perspective, powders offer an advantage because their ingredients can be prepared and combined while remaining separate as solids. You can often spot several kinds of granules in laundry powder.

What's in laundry liquid?

Water is the principal ingredient in laundry liquid. Every other component must be selected carefully, as it needs to remain stable in the bottle before functioning alongside the other ingredients during a wash.

These ingredients are similar to those used in powders and include alkaline salts, metal sequestrants, water softeners and surfactants.

In liquid products, surfactants are commonly identified as ionic, meaning charged, or non-ionic, meaning uncharged. Since non-ionic surfactants can naturally be liquids, they are unsuitable for powder formulations. They suspend oils effectively in water and do not create soap scum.

Liquid detergents additionally need preservatives to stop microbes growing and spoiling the mixture.

There are microbial consequences inside the washing machine too. Liquid products cannot include the peroxides, or mild bleaching agents, used in powder products. Peroxides destroy microbes. Without peroxides in liquid detergents, mould biofilms are more likely to develop in the machine, while bacteria can be passed from one clothing item to another.

Instead of peroxides, liquids will generally rely solely on optical brighteners.

Liquid detergents do, however, have an advantage over powders: they may be applied directly to stains before the garment goes into the wash.

A more recent “convenience” format for liquid detergent is the highly concentrated pod. These colourful products can resemble sweets and have been shown to pose a danger to young children and people with cognitive impairment.

Pods also take away the ability to reduce the amount of detergent when doing a smaller load or whenever you simply wish to use less.

So, what about enzymes?

Enzymes are proteins that evolved naturally and are added to laundry products to tackle particular stains. In chemical terms, they are catalysts: substances that accelerate chemical reactions.

Their names identify the molecules on which they act, followed by the suffix “-ase”. Lipase, for instance, breaks down fats, or lipids; protease breaks down protein; and amylase and mannanase break down starches and sugars.

These enzymes come from organisms in cool-climate areas, enabling them to work at the relatively low temperatures of wash water.

A wash cycle that is excessively hot may damage, or denature, an enzyme’s structure, preventing it from helping in the wash. Consider how a translucent egg white turns white during cooking – that is protein denaturing.

When a detergent contains enzymes, the wash temperature should not be either too high or too low. Standard laundry tests generally use temperatures of 15–20°C as a guide.

Is powder or liquid better?

Consumer decisions are shaped by performance, psychology, price, fragrance, environmental concerns and convenience.

Trying different products is worthwhile to establish which suits you best and meets your needs, household budget and environmental preferences, including recyclable packaging.

Personally, I wash at 20°C using half the advised amount of a nicely scented laundry powder in recyclable cardboard packaging, containing a broad selection of enzymes and an activated peroxide source.

A little knowledge of chemistry can make a considerable difference when it comes to clean clothes.

Nevertheless, detergent manufacturers do not always provide a complete ingredient list on their packaging.

For further details about a product’s contents, you will need to visit its website. You can investigate further by consulting documents known as safety data sheets (SDS). An SDS is required for every product that contains potentially hazardous chemicals.

Nathan Kilah, Senior Lecturer in Chemistry, University of Tasmania

This article is republished from The Conversation under a Creative Commons licence. Read the original article.