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Is it better to use a Washing Powder or a Washing Liquid

There are an abundance and confusing amount of washing detergents on the market today and the purpose of this post is to examine the differences between washing powders and washing liquids

What are they made of?

There are, broadly speaking, a couple of different types of powder and liquid.  There are powdered and liquid detergents and powdered and liquid soaps.  This is only a broad categorization as many washing detergents contain both soap and detergents.

However, the difference between a soap and a detergent can be defined as follows

The fundamental difference between soaps and detergents is that soaps are produced from a fat or an oil combined with Sodium or Potassium Hydroxide, while detergents are made from synthetic ingredients.

That aside, powder and liquid washing detergents essentially contain the same ingredients. The biggest exception is that powders often contain bleach, and additional ingredients to adhere to liquid surfactants in the powdered product [1, 2].

For example, look at the table below.  It shows the shows the similarity between a typical Powder and Liquid (correct at the time of writing) [3].

Differences in Ingredients Between Powder and Liquid Formulations
Powder Liquid
5-15% Anionic Surfactants 15-30% Anionic Surfactants
Nonionic Surfactants 5-15% Nonionic Surfactants
<5% Enzymes <5% Enzymes
Soap Soap
Optical Brighteners Optical Brighteners
Phosphonates Phosphates
Perfume (Butylphenyl Methylpropional, Geraniol, Hexyl Cinnamal) Perfume (Butylphenyl Methylpropional,

Geraniol, Citronellol)

Polycarboxylates (water softeners) Polycarboxylates (water softeners)
Zeolites (builder, to soften water and adsorb surfactants)
Oxygen-Based Bleaching Agents

 

These are the only ingredients listed on the label, but the unlisted filler is the biggest difference between formulations. Generally, in liquid formulations, the ingredients are pre-dissolved and stabilized in a suitable liquid (e.g. water), whereas powders need to dissolve in the washing machine and so use soluble fillers (e.g. sodium sulfate). 

How are they made?

A powdered or liquid soap is made by combining an oil or fat (a triglyceride) with an alkaline to liberate the fatty acids.    The ‘soap’ or ‘surfactant’ action of soap is due to fatty acids.

To liberate the fatty acids from the oil, the raw triglycerides need to be heated with a strong alkali. Both sodium hydroxide (lye or caustic soda) and potassium hydroxide (potash) are commonly used as the strong alkali. Sodium Hydroxide will often produce a solid lump of soap whereas Potassium Hydroxide will produce a liquid.

The reaction forms fatty acid salts, which vary in texture depending on the alkali.

Animal Fats Plant Fats
Raw Animal Fat Resulting Fatty Acid Raw Plant Fat Resulting Fatty Acid
Tallow (beef fat) Sodium/Potassium  Tallowate* Palm Oil Sodium/Potassium Palmate
Lard (pig fat) Sodium or Potassium  Lardate* Palm Kernel Oil Sodium/Potassium Palm Kernelate
Laurel Oil Sodium/Potassium Laurate
Olive Oil Sodium/Potassium Oleate
Coconut Oil Sodium/ Potassium Cocoate

 

Detergents are a different product entirely.  While solid and liquid soaps have been manufactured using the same fundamental method for centuries, making a detergent is a different synthetic process altogether.

A document available on the American Cleaning Institute website (an organization representing the cleaning industry), summarizes how powder and liquid detergents are manufactured [4]. In summary:

  • Powders – dry and liquid ingredients are mixed into a slurry, which is heated, and spray dried into granules. Heat-sensitive ingredients (e.g. enzymes, fragrances) are then added to the product before packaging to prevent degradation.
  • Liquids (and gels) – dry and liquid ingredients are continuously mixed to ensure uniformity and stability of the final product. The mixed product is then packaged.

So is it better to use a liquid or a powder?

In the US, liquid detergents are the most popular washing products, with pods rapidly gaining market share, and powder sales declining.   In the rest of the world, up to two-thirds of the population all over the world simply uses the powder form of detergent.    However, powder sales are generally on the decline worldwide.

Soap washing products are less abundant, but their use is increasing exponentially, particularly for those with sensitive skin and allergies.

  1. Powder Detergents
Pros Cons
· Generally cheaper

· Eco-friendlier cardboard packaging

It weighs significantly less, what makes it a lot easier and cheaper to transport

· Weigh less, so lower transport costs

· Often contain bleaches, which whiten clothes

· Can need warmer water to dissolve

· Can leave residue in machine drawers

· Sodium sulfate can disrupt septic tanks

· Can be easy to use too much, leaving ‘gunk’ over clothes

· Detergent dust can be an allergen

 

  1. Liquid Detergents
Pros Cons
· Pre-dissolved, and so may use cooler temperatures

· Can pre-treat by pouring on clothes

· Don’t commonly contain bleaches

· May be less likely retained on clothes, causing less irritation

· Usually more expensive

· Packaged in plastic, less eco-friendly

· Can have poorer stain removal, due to a lack of bleach

 

  1. Soap Powders
Pros Cons
· Can be better for those with allergies

· Some products can be used in cold or lukewarm water

· Less likely to disrupt septic tanks

· Traditional method of washing

· Eco-friendlier cardboard packaging

 

· Generally, more expensive than detergent

· Can form a soap scum, that need to be washed away

· Risk of strong alkali if not properly manufactured

· Can require additional washing machine maintenance

 

  1. Soap Liquids
Pros Cons
· Can be better for those with allergies

· Weigh less, so lower transport costs

· Pre-dissolved, and so may use cooler temperatures

· Less likely to disrupt septic tanks

· Traditional method of washing

· Generally, most expensive washing products

· Packaged in plastic, less eco-friendly

· Risk of strong alkali if not properly manufactured

 

 

There are pros and cons to liquids or soaps.  I personally prefer to use a powder, primarily because the packaging is typically cardboard as opposed to plastic.  It is cheaper and more eco-friendly to transport.  It’s typically cheaper to buy.  And I have sensitive skin so my preference is a powdered soap of some sort.  I just make sure I use a bleach-free formulation.

However, this is an entirely personal choice.  There’s no right or wrong answer here.

What do you use and why?

References

[1] Smulders, E., von Rybinski, W., Sung, E., Rähse, W., Steber, J., Wiebel, F., & Nordskog, A. (2007). Laundry detergents. Wiley‐VCH Verlag GmbH & Co. KGaA

[2] Bajpai, D. (2007). Laundry detergents: an overview. Journal of OLEO Science, 56(7), 327-340.

[3] Unilever. (2018). Persil Products. www.persil.com [Accessed: 6/2/18]

[4] American Cleaning Institute. (1994), Soaps and Detergents. www.cleaninginstitute.org [Accessed: 6/2/18]

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